I've done sxsw for 4 years, fun festival. I'm actually more interested in the Film and Interactive portions of it - Once the music portions start, all the fucking retards come out (this, however, includes the scantily dressed sluts, so I can't complain too much), and free stuff is a lot harder to come by. I think what I like about SXSW is that during the day you are "business" more or less, going to panels and events, networking, etc. Once the night-time comes around, it's party your asses off.
All said, I come away with a shitload of free stuff (easily 10-15 tshirts I only wear at the gym, some headphones, and bags full of your typical printed crap) and about 2 weeks of free food and booze. This year the Wife walked away with with a Beats Pill, which is pretty dang nice. A couple years ago we got about 4-500 dollars of software we ended up selling on craiglist.
One thing I've learned that vendors should take heed of: If you're trying to attract people to your party/event/area, free food will trump free booze, always.