Great designs for t-shirts. My favorites, and why:
4. Bueller - top design -- I like the retro multi-line look, and I like the fact that it says "GEEK HACK" on the front, and 'DOT ORG' on the back. Fit 'keyboard enthusiasts' in there and it might even be better. It's a nice bold, simple design. Work a v6.0 in there somewhere, somehow, and it's great.
7. Lastpilot -- my favorites are the Dodgers font design in the upper left corner -- very retro, and it's got a keyboard in the design! The next favorite is the second row, second column. It's simple, and features a keyboard. It would be better if it featured a ".org" but it's still nice and clean, and graphic. Missing a '6' to commemorate GH's sixth birthday, but still great designs.
12. Strafe -- I like the '6' superimposed over keyboards, that's great. I think if you combined that with another designed logo, and it would be even better. Still, a nice clean design, and so far works in the sixth anniversary theme the best.