It all depends on where you go around here.
I'm from Canada (Toronto area) and have been to Prereleases in 5 different cities--Oakville, Mississauga, Barrie, Oshawa, and Orangeville--and the results of each are mostly similar.
In all of them, you pay $35 and get 6 packs to construct your deck. You also get the usual promo card and sleeves. After the tournament, everyone gets an extra 2 packs from the set. The first place person usually gets an extra pack.
In some of them, you get a poster for first place (sometimes second place gets one too).
In one of them, they gave out a theme deck to the first place winner as well.
The two that gave out the extra stuff (the theme deck and posters) is run by one organizer and the other 3 are run by another organizer. The ones that give out the extra stuff are further away from me and I've only started going to them recently. It figures that when I got first and second place, it was at the prereleases where they didn't give extra stuff.