Like everyone else so far I would definitely say "pace yourself". PP is a chance for me to see one of my only other surviving friends from the high school days - so our first night in town usually results in massive hangovers
Definitely take advantage of any free breakfast at the hotel you are at. It IS worth it to drag your weary carcass there, because like many have said - odds are you wont be eating much once things start up.
Do say hello to anyone & everyone. I suck with names (who now Alzheimer's hit at age 40, maybe I'm just special) but I do recognize people from year to year (this is only year 3 for me). This is quite a collection of good people - from all over, and their tastes are pretty diverse. You're bound to meet some good folks here for sure.
Bring cash. You never know where you'll find an ATM, or if your fellow PPers have already drained it - and you will find that one item you can't live without at one of the vendors. Also, taking out a bunch of cash at your local bank before heading to ATL can save you precious dollars in fees - could be the difference between having that one extra beer (or cd etc) each night.
If you hear of a "meetup" or something and you are available to go. Again, the people that attend are a big part of why this has become such a special event. Whether it's lunch at Front Page News (which we were at, at same time, but didn't sit with the big group) or if you hear a bunch of people going to Six Flags, Cheetahs, the Coke museum etc - see if you can bum along. You'll have a blast and end up getting to know some of the people a lot better.
Listen for kickass tunes emanating from behind hotel doors. If you hear something you like - knock, introduce yourself & be prepared to party.
Finally, if this is your first PP Fest, the number one piece of advice I can give - be prepared to be hooked immediately. Start planning for next year - tell your boss/significant other etc, start saving money now
See ya there,
Jeff