As for the comments someone made about the iMac screen being crap - nothing could be farther from the truth! The screen is gorgeous! And I say this as someone who never thought they could ever use a glossy display until I went to view the iMac prior to buying it... Some people just can't accept glossy displays ( I thought I was one of them) but after seeing it in the flesh I was sold on it.
So, in summary, now is as good a time as ever to buy an iMac. It is very unlikely to be upgraded in the near future (maybe same time next year) so if you want one then just buy it now - you won't regret it!
I laughed out loud when I read that my 24' iMac screen was crap. I just walked through Best Buy and thought how much more gorgeous my screen was then the majority of other monitors.
The average consumer like me does not need Quad Core. I can rip a dvd with handbrake, watch a movie on iTunes, have Hulu full screen, mail app, safari and firefox, VLC, and video chat all at the same time with out making my 24' iMac stutter. I did all this just to test the system and it's a beast.