I tried 64 bit Debian about two years ago when it was very new, and decided that I should stay with 32 bit for the time being, but recently I have been in an organizing frenzy, and thought that instead of just reinstalling the 32 bit version I should try 64 bit again. More here
I have to say that support for 64 bit architectures has improved quite a bit since my last attempt. There is now a native 64 bit flash player, and I have not yet found an important program that I used in 32 bit that is not available in 64 bit. In addition to the change from 32 to 64 bit, this also gave me a chance to organize things better on my computer, which was the real tipping point for me. I just seem to be in spring cleaning mode.