Well according to the front page of MacRumors:
"This likely doesn't change anything for future planning as Apple will certainly adopt Intel's upcoming Nehalem processors over time. Nehalem is expected to offer a dramatic performance boost over existing processors. These next-generation Intel processors will be first launched for servers in Q4 2008, and come to desktop and mobile platforms in 2009."
^^Well I don't know for sure if that means the new iMac updates will come out in '09 but that sure is what I understood.
I'm in a position wether I should buy one now or wait for a November "speed-memory-bumps" update, which is unlikely since nobody really knows. I'm in a desperate need of a new Mac and it's driving me nuts. Wait to get the most bang out of my buck or buy now and a couple of weeks something a lot better will come out...hmmm.
It doesn't seem likely that there will be an iMac upgrade before early next year. With the traditional holiday shopping period just around the corner it wouldn't seem like a good time to introduce new iMacs.