Yeah, I like my dual core. My reasoning behind it in this particular case is.........why not?
It certainly won't hurt performance and you'll be ready for one more apps and games become multithreaded. However, that won't exactly happen overnight and it probably won't be atleast until Vista comes out that you'll see dual core optimizations exploding.
Right now with XP there is only a little 'dual core hotfix' that was thrown together to fix certain issues but XP doesn't really support dual cores nor make use of them.
I'm sure this is something that will be addressed in vista and should hopefully make complete use of dual cores.
Next gen gaming will definitely be making use of the two cores, the main thing that'll start needing to catch up will be the rest of normal software programs.