Didn't see this thread, but I just posted a new thread detailing my reasoning for thinking the iMacs won't see an update until probably April. I'll copy and paste it into here for simplicity. Hopefully the moderators don't mind, if so you can delete my thread on the iMac forum:
I was looking at the buyer's guide, which lists the avg update time as 185 days. However, I looked at all the updates listed going back to 2003 and thought, since this is obviously only going to be a speed bump, how long is the average cycle for speed bumps alone? I would expect that since a re-design would take longer than a speed bump, I thought it would give me more reason to think that a speed bump is imminent. Unfortunately that wasn't the case:
If you take out these spans:
09/03-11/03 - Added the 20" model, rest stayed the same so not really an update
11/03-08/04 - Introduced the G5 iMac
10/05-01/06 - Introduced the Intel iMac
09/06-08/07 - Introduced the Aluminum iMac
All that's left are spec speed bumps. Averaging out the times between those, I got about 215 days, not 185. Granted, if I keep the switch to Intel into the equation, since it wasn't really a redesign, it brings it down to 190 days, but the Intel switch was an extenuating circumstance, so I don't think it should be considered.
So if we take 215 days as the average, it means we have about 2 months left (on average), i.e. March. If you look at all of the mac products in the buyer's guide, you'll see that Apple, at least in the last 5 years, has only once updated a product in March, a quiet update for the 30" display. There's also only been 3 updates during February for the last 5 years, and only 1 update in the last 4 years if you take out the xserve and iMac which were both updated in February 2003 (the mini got it's Intel switch in Feb 06). 8 updates have occurred during April in the last 5 years, with at least one product update every year during that month.
Of course, none of this might mean anything at all, but merely on a statistical standpoint, if I had to place a bet, it would be for April or May (which is unfortunate because I'm going to be buying soon and I'm hoping for an update)