...if you show up with a GPS direct to your destination, you'll fail your oral before you even get into the plane. Your DPE will not let you use the GPS when you fly the first 2-3 waypoints of your simulated XC. Most will ask you to fly direct back to the airport when you're done with maneuvers, etc... saying something like, "Take us back to KXXX..." and then you can use your GPS. They want to see at some point during the ride that you know how to use it...
In the 'real' world you'll find that your trips across the state or what not will be more like GPS direct flights. But the point of putting together a NavLog for your PPL checkride is so that you can demonstrate pilotage/dead reckoning skills. You'll need to do 10 minute or so waypoints all the way to your destination.
Look at page 101 on the PTS:
Task A: Pilotage and Dead Reckoning (AMEL and AMES)
References: FAA-H-8083-25; 14 CFR parts 61, 91; Navigation
Chart.
Objective: To determine that the applicant:
1. Exhibits satisfactory knowledge of the elements related to
pilotage and dead reckoning.
2. Follows the preplanned course by reference to landmarks.
3. Identifies landmarks by relating surface features to chart
symbols.
4. Navigates by means of precomputed headings,
groundspeeds, and elapsed time.
5. Demonstrates use of magnetic direction indicator in
navigation, to include turns to new headings.
6. Corrects for and records the differences between preflight
groundspeed, fuel consumption, and heading calculations
and those determined en route.
7. Verifies the airplane’s position within 3 nautical miles of the
flight-planned route.
8. Arrives at the en route checkpoints within 5 minutes of the
initial or revised ETA and provides a destination estimate.
9. Maintains the appropriate altitude, ±200 feet and heading,
±15°
http://www.faa.gov/training_testing/testing/test_standards/media/FAA-S-8081-14B.pdf
