let me ask the question another way
When have you had inadvertent(or better unexpected) ice, what conditions existed, what did you do?
Has anyone been in freezing rain? What conditons? What did you do? I have heard the power on ILS stories.
I'm flying a "fully deiced" (i.e. has all the equipment but was never tested or certified because that wasn't required when the type was certified) twin and encounter ice fairly often in the winter. My goal is to always find a way out of the ice as soon as it starts to build and if I can't exit by the time my IAS has dropped 20 Kt I'm gonna be looking for the nearest suitable place to land. Prior to this airplane I had a Bonanza with nothing more than a heated pitot and a marginal windshield defroster. I did get into ice with the Bo a few times but accumulated more than an inch using a similar but more conservative methodology (i.e. avoiding cold clouds and postponing more trips).
There are four categories of icing strategies and techniques: planning, inflight avoidance, escape, and coping.
On the planning side there are a lot more resources today than in the past but it's still nearly impossible to get a clear answer to the existence of ice on any given trip much of the time. More often than not it comes down to whether or not there is substantial evidence that ice will be a problem. If you can get pireps along and upwind of your route and there are multiple reports of light to moderate or worse at altitudes you need to fly, if there's any report or forecast of freezing precip, or if it's raining and the freezing level is too low to fly beneath you've got plenty of reason to stay on the ground (deiced or not). Other than that, it's a rather grey area, and the decision to make the attempt should consider the consequences of aborting or diverting the flight and involve the identification of one's "outs". Many pilots will tell you that you should always have "an out" but my philosophy is that you should never go without at least two because it's all to likely that at least one will prove to be unavailable when you need it. Starting with two and executing one if the other disappears should keep you safe since the odds of both going away at the same time are pretty small. And that's the primary reason I wanted an airplane with deiced wings, props, and windshield: the equipment is one of my planned "outs" so I only need one more to minimize the risk. Other examples are at least a thousand feet of above freezing air above the ground (in the flatlands), an airplane with great climb performance and known clear skies above a relatively shallow layer of clouds, turbocharging and weather you can top from the departure without getting into any clouds, VFR conditions below the clouds, to name a few. And it's worth mentioning that for the most part this is about flying outside mountainous areas because the icing issues are far more complicated when the terrain is tall and rough and mountains tend to eliminate a great number of potential outs available elsewhere. Finally, part of the planning process should be identifying areas where ice is most likely such as downwind of large bodies of unfrozen water, the NE quadrant of a low pressure area, and downwind of upslope terrain relatively perpendicular to the wind. You also need to consider increasing your fuel reserves. If you do pick up any ice it will slow you down and/or require extra power. Staying above the clouds often means fighting more headwind than you would otherwise have to deal with. Finally, plan to make the trip in daylight. It's far more difficult to avoid clouds at night and the lack of sun means you probably won't be able to lose any ice above the clouds.
Inflight avoidance tricks at the departure end include climbing through holes, zoom climbs, and staying below the clouds. Enroute you can deviate around clouds if ice is likely (you can sometimes dip into one briefly to determine if that's the case), cruise over the tops, fly at an altitude where the OAT is colder than -20C, fly low enough that the air is above 0C or you're below the clouds, or fly in snow (snow generally does a good job of sucking up all the unfrozen supercooled water but the tops of the clouds producing the snow often generates ice as well). Since high altitude is involved in many of these methods, supplemental oxygen and a pulse oximeter should be considered mandatory if you're counting on them. One of my favorite tricks to stay above a mid level cloud layer is to ask ATC for a 1000 ft block altitude as this can minimize the necessary height to remain cloud and ice free in many cases. If there are ice issues at the destination don't let ATC push you down into the ice prematurely. If you tell them you want to stay above the clouds as long as possible for ice avoidance they will generally be accommodating. It helps if you offer to accept indirect vectors while remaining up high and also let them know what your plan is (e.g. "I would like to stay at 5000 until 15nm from KABC"). It's also a good idea to plan your route to avoid any nearby Class B where ATC's flexibility can be limited even if that means not landing at the closest airport to your ground destination.
Then there's the escape issue. If your deice is limited to pitot heat you should initiate an escape the moment you see ice accumulating or sooner (you might want to execute an out simply because you can't avoid the clouds like you planned). For an unprotected airplane in level flight the best exit is often directly behind you, if the air there was ice free a couple minutes ago it probably still is. Getting below the freezing level is almost always a good way to escape if that option exists, but to keep on top of that one should be checking the surface temps along your route continuously. ATC, especially approach control, can often tell you the current freezing level in their area. If they don't know they can ask another pilot that's arriving or departing. Except in the vicinity of an active frontal system you can almost always escape ice by changing altitude by 3000-4000 ft but if that leaves you in the clouds the ice you've already collected will not sublimate. If you can get above the highest clouds into the sunshine whatever ice you picked up will slowly dissipate but it can take as long as an hour to shed it completely. In anything worse than trace to light ice most NA airplanes won't be able to climb more than a few thousand feet since even a little ice significantly erodes the ability to climb. If climbing is one of your planned outs, you should execute that option early and be prepared to switch to out #2 as soon as you detect much performance loss. Keep in mind that switching to airways from a direct leg often lets you get a lower altitude as does flying in areas served by approach control (this info can be used when planning the flight as well).
On the coping side of things, there are some useful tricks to minimize the effects of ice as well:
Cycle the prop rapidly over a few hundred RPM every few minutes. This flexes the blades breaking off some of the ice.
Pay attention to the MP and activate carb heat or alternate air if it drops at all. On some airplanes it's best to switch to heated or alternate air anytime you're picking up ice.
Keep your speed up. Ice raises the stall speed by an unknown amount and can make recovery impossible. Don't use flaps if there's any ice on the tail (hint: if you have any ice on the wings the tail is probably worse).
If you are landing with ice, use a runway that's twice as long as you normally feel comfortable on. You will be coming in a lot faster than normal (extra speed for no flaps plus extra speed to avoid stalling) and the runway might be slippery.
If you must fly an approach and are carrying ice or expect to pick some up on the approach, assume that a go-around is NOT possible and plan accordingly. Diverting to a "big" airport for an ILS with the full Monte approach lights into a long wide runway is probably in order.
In a retract, you may need to leave the gear up until you're almost over the runway in order to get there but don't forget to lower it before touching down! If someone is riding with you, ask them to remind you about the gear when they see the runway. In such a situation it's likely you'll be carrying enough power to defeat the gear warning.
Don't even think about making a smooth or full stall landing but try real hard to avoid touching nosewheel first. Remember that the plane is likely to feel quite different than normal in the flare (you may not get much of a flare either).
