There will be some informal going on I'm sure. The official practice sessions are $4 though, we have to charge so that we can have guaranteed space available to us for this. We've been able to just sort of "squat" in the past but word is that's not viable so much this year.
I would not let the price deter anyone though if they want to attend the practice session. In case of emergency I will give someone $4 worth of generic tickets(subject to me running out of generic tickets.) This event was my idea, both years I've done Gen Con my #1 wish I hear from players is "I wish I'd been able to get more games/practice in." So here it is, a chance to sit down and practice. The judges will even take a look at books and offer advice as well as help newer players be prepared for what competing at Gen Con is like. We will bring a host of different books so you can practice against whatever mage you'd like.
Also the other main advantage is if you don't have the contact information for other players and you don't make plans in advance you may never find the casual play. So for all the first time Gen Con attendees here is is, listed and scheduled easy to find.