I'm sure the IRS will eventually crack down on that as well.
I know a lot of people are upset at the crack down, but if you are doing business electronically you are technically supposed to be reporting that income.
The part that bothers me is that my wife and I occasionally exchange money through such devices to pay each other back for purchases, etc. Or if her and her co-workers get lunch together, she may pay and they pay her back through electronic means. They say they aren't going to track and tax that...but just wait. Or wait until that becomes a major tool in law enforcement. You friend gets arrested for doing something bad, but you sent him $20 via Venmo for lunch and now they think you are a customer.
Ultimately the government wants to track every transaction between every person, so they can get their piece of the pie and document your every move, and cash makes that nearly impossible.