I've lived in Downtown G'ville for a million years, so here's my take on parking: don't do it if you don't absolutely have to. The best way to roll is to park your vehicle where you are staying and leave it there the entire weekend and walk/bike/bus/taxi/downtown. Once you're there, 75% of the venues are within a 3 minute walk. The other 25% are within about a 12 minute walk. The Holiday Inn is about 15 minutes from everything.
The bus system here is actually pretty good, and buses run regularly Wed. through Sat. until 3am. Unless you are staying way out by the interstate, this may be your best option. Check out the routes here: http://go-rts.com/
. Single fare is $1.50 or you can buy an all day pass for $3.
Be advised that cab drivers here are largely scumbags, and you will pay Manhattan prices to get anywhere during Fest if you can flag down a cab at all.
If, for some crazy reason, you NEED to drive:
1) Make absolutely positively sure that you are not in a tow-away zone. Seriously.
2) Have a designated driver at all times. Seriously.
3) There is a pay garage at 105 SW 3rd Street, but that it isn't all that cheap and can get full quickly. (Plus, dickheads like to shoot each other in there every once and a while.)
4) Here is the local secret. Everyone tries to park right next to the venues or west of downtown (Towards the Holiday Inn). If you drive 4 or more blocks northeast of main street and university avenue (i.e. behind the Atlantic), there is virtually unlimited, free, on-street parking. Obviously, don't leave valuables in the car, but the neighborhood is pretty high end and safe.
Hope this helps