There used to be 2.4GHz P4's with a 400FSB that would overclock real well, but unfortunately for me I haven't seen any in at least 2 years now.
I've got the two memory slots. Both are being used right now although one has a 256 while the other is a 512. I could bump that up, but considering the rest of the computer I don't really see much point in it right now.