Sometimes I preorder but only for titles I know will sell out and I won't get on time. What I have seen at Wal-Mart is that when you pre order a game there, you get a free $10 gift card when you pick up the game. I saw that when I went to get ME2 from there. Didn't preorder it though.
Back a few months ago when I got ODST, I preordered from Target and got a free $5 gift card, and it was only like $1 to preorder. So I got like 4 bucks from preordering it there. I don't know how much it is to preorder at Wal-Mart though.