Just thought I'd chime in a little bit here, partly because I just like hearing other people's reasons for waiting for an 8 core or getting a quad core now.
Personally, I'm holding out to see what the octo core system brings. Judging by the price for ordering one at Dell, I feel like I have a fairly good idea of how much it'll cost; and if it does indeed get priced in that range, then the money I've been saving can cover it.
Why am I waiting? Well, I don't *need* a new computer, although I do push my MacBook Pro to its limits fairly often. I don't do anything overly processor-intensive on a normal basis, although I do process a lot of 8MP RAW photos and re-encode videos from time to time. My computer stressing comes from sheer multi-tasking, which will also require a lot of RAM on my part. Even now with 2 screens (15" MBP and 24" Dell) I keep a lot of programs open so I can do several things at once. When I get a Mac Pro, I'll be getting 2 more 24" displays to complement the one I have for use when working.
Having said that, I'm not *definitely* going to get an octo-core system. If the price is significantly more than the current quads, then I'll be forgetting even trying. Additionally, depending on just how much more they'll be, I may get a quad at that point since I imagine their price will be lowered at least a little (I hope). Plus, I'm lucky enough to be eligible for the education discount for a while longer, so that will help me out a lot as well no matter which way I go.