Here's some advice from a crew member. If you want to TRULY experience all that the festival is, then you need to get into a hotel adjacent to the venue. Others may disagree. And that is their prerogative. However, I believe that the social aspects of the festival are just as much a part of the total experience as the music. You will want to stay as close as possible to get the most out of PPUSA.
Basically, I know of four. I am quite sure there are others. But these leap to mind. And all are within easy walking distance of the venue.
Artmore Hotel
Marriott Atlanta Suites Midtown
Residence Inn Atlanta Midtown
Hilton Garden Inn and Homewood Suites Midtown
If you want to get into one of these, book as soon as possible. They will fill up. If you DO get into one of these places, then park your car in the hotel garage when you arrive and forget about it. You won't be needing it - unless of course you want to take in some other sights while in Atlanta...or ATL as all my gangsta dawg wigster homies like to say...shout out to my posse yo!
Now, having said all of that, this is VERY important. If you can't get into one of the hotels within walking distance for any reason, then staying Midtown is not - repeat - NOT worth it in my opinion. The rooms are too pricey and you will end up missing out on the social aspects of the fest anyway. And trust me, walking alone 6-8 blocks to a hotel in Midtown at 1-2 am is NOT a casual stroll...if you get my drift. My advice? If you can't stay close (and you don't pack heat) then get a nice room convenient to an interstate exit 15-20 minutes out and pony up for the $10 a day parking fee at the venue. You can easily make up the parking in what you'll save on a room.
Other advice?
1. Bring money for CD purchases. You asked what the CD sales are like? Ok. Here it is in three words...HEAVY METAL ORGASM! More prog/power/death/black/melodic/gothic/symphonic/orchestralmanoeuvres/folk/viking metal CDs than you have ever seen in one place. Unless you've been to Wacken or one of the other big euro open air festivals...in which case I hate you already.
2. Bring money/make time for FOOD. There are some great restaurants in the area around the venue. Others are a short cab/MARTA ride away. Anything and everything you could want. I will not plug a favorite restaurant here *coughfrontpagenewscough* I'm not that crass. Besides, not everyone appreciates some of the BEST CAJUN FOOD in Atlanta.
3. Drink a LOT of water. Even if you don't imbibe of the various liquid libations making the rounds (have you ever seen a moon shine that bright?) you WILL get dehydrated unless you drink water and LOTS of it.
4. Take Airborne like religion for three days leading up to the fest and continue to take it until after you get home.
5. Bring hand sanitizer and baptize yourself in it on a semi-regular basis all day long every day. Seriously. The ProgPower Plague IS a very real thing and it is no joke. I have seen it kick BIG grown man ass...and it is NOT pretty.
6. Enjoy one of the best festivals of any kind anywhere!