Is gaining vehicle skills affected at all by pulling off risky manoeuvres?
Solution 1:
I believe there is no factor for doing stunts, it's just the distance covered that counts.
However I could find evidence both for and against the trick theory (none of them 100% reliable, mind you)
- For: http://www.tomshardware.co.uk/forum/105768-13-andreas-increase-driving-skills
- Against: http://gta.wikia.com/Statistics
If I remember correctly, it was a viable technique to level up these skills by jumping a vehicle onto a flatbed train and letting it carry you around the map for a few (or for lots of) rounds.