Take a yoga class or go to one of the free yoga days at the Hays St.
Do one of the collective bike rides downtown or a pub run. Go to a PechaKucha, where you'll see lots of young, successful, smart types. There are tons of gallery openings and events at Artpace, SAMA, and the McNay with a decent-looking crowd. Mary's strip, or even way out in 1604-land. In SA, check out the bars in Southtown, the Pearl, the N. And, I'm afraid that bars are where young people go to meet others in both cities. Online scene is better in Austin, but people in that city are always looking over their shoulder for the better/cooler person. (I'm attached now.) I think the online scene here is less than it is in other cities for a couple of reasons: less tech-savvy population, and more fear that you'll be spotted by folks you know, as there's not much anonymity here (i.e., everyone seems to know everyone). I've found this a very easy city to meet people, but not all of them were what I was looking for.