The weather (infrequently), the people (invariably) what with naked cowboys and everything;))
The hottest things for me were the location based networking apps like Glancee and Highlight. Robert Scoble writes more eloquently than I can on the topic, his post is linked to with my comments on my Google+.
But, at the end of the day, SXSW is, of course, all about the people. I feel so privileged to be able hang out with some of the brightest and best the world has to offer. Until next year….