I was just debating this to my friend. He's finishing up a 347 job on his car and filled all the engine bay holes and everything is coming together really nice but he's unsure if he wants to put the AC back in. I'm a little torn between it myself. For my car, when i got it the AC was trashed...lines were already cut and it needed a lot of work, and i was wanting to cut weight so i ditched it. On his car, he's going to be making a crap load of power and his car is SO nice that i told him to keep it. I mean why not? In the end i think he decided to remove all the major parts and store them, and run a short belt for a while. You can always reinstall it later if you keep all the parts and plug the lines in the car and do it right.
That said, i would say if your AC is in nice working order and you're not going racing, keep it. If it's ragged out and needs a lot of work....screw it. I like driving with the windows down anyways, but if you get caught in traffic on a hot day it's nice to have.