I whole heartedly agree. If the iMac is updated now, it will be a still be core2duo, or maybe a core2quad (not likely), and that is basically no improvement over the current model. It is old tech and an old architecture. While core2 is still a great architecture, there is no doubt Core i7 is the way forward, but a mobile version will not be released until the later part of 2009. iMacs use mobile processors, so no i7 for this release, and unless there is a major change, why would you be upgrading?
The same thing happens every time a new machine is due, people sit here and speculate and build up in their mind a massive machine that will never see the light of day, and when reality hits, we all feel ripped off. Apple can never live up to expectations of the fanboi's. Until there is an i7 mobile processor, don't get excited about and iMac upgrade.
I am holding out for new Mac Pros later this year, likely to be May / June at the earliest, and I wouldn't be surprised they hold off and release the new Mac Pros along side Snow Leopard.
If you want to get excited about an upgrade, 10.6 Snow Leopard is what you should be looking forward too. This will certainly make your current iMac run a heap faster. New finder (i am in heaven) and slimmer apps, and highly optimised code. That is an upgrade worth having.
now is a perfect time to simply bump hd sizes & ram at the same prices to give the imac a boost then bump with i7 before christmas.