Unless you are in a UT fraternity or sorority, a lot of the bars with a Sixth Street address are pretty lame (one exception off the top of my head is The Jackalope). Check out the bars along Red River for a more interesting experience. However, on Friday and Saturday nights, the police block Sixth St. to cars, and people can just hang out in the middle of the street. This is a sight to see, so I recommend walking down Sixth St. during these times, for pure entertainment value. \r
Also, whatever you do, DO NOT eat Roppolo's pizza. This is quite possibly the worst pizza in the United States. This should be fairly obvious upon sight of it, but I too have reluctantly purchased a plastic-y looking slice of cheese at 1:00 am, just because there are almost no places to get food late at night downtown. \r
If you find yourself really needing some food, you are MUCH better off walking to the Onion pizza place at 116 W. 5th (not far the center of Sixth St. mayhem). Or just ask some locals where you can find the guy selling the authentic Chicago style hot dogs out of his trailer. Trust me on this.