I've been looking through the forum a bit and I didn't see anything mentioning this very useful tactic.

Whenever you pay someone to train a skill, the money goes into their inventory. So if you have decent pickpocketing, you can steal the money right back. This is useful in two ways: 1) Obviously, you get free skills without hacking or cheating in any way. And 2) stealing that amount of gold will make your pickpocketing skill absolutely SKYROCKET. I levelled my pickpocketing to 100 within the first day I played the game, easily.

Now i get to steal clothes off people's backs and watch them walk around town in their underwear. This game is great.

You can also do this if they are a companion, you can access the gold in their inventory. So you can pay them, train, take the gold back & repeat. I suspect this may be fixed in a future patch though...