Austin IS the most liberal city in Texas. It's where all the "hippies" live. BUT, I am a little bit conservative an have found that as long as you have an open mind, anyone can be happy here! I like to say that there is something here for everyone.
As far as the bar scene goes (not that you asked, but I'll tell ya anyway

), 6th street is LOTS of fun! There are also some popular places around campus. There's an awesome bar where all the greeks seem to congragate (read: cute frat guys hehe).
I think the bars in San Marcos close at midnight.