It's getting pretty tempting to leave Canon. I never thought I'd say that!
Um, well... I can't say I would agree with you on that. I have once said I will never, NEVER, switch to Nikon, ever, period! And I feel the same way today as I did then. 
Anyway that being said, as beautiful of a camera the 5D2 is, it is due for an upgrade. I can only assume that Canon will blow the D600 away by making the best full frame "compact" DSLR anyone has ever seen! I just hope the rumors of a "cheaper" plastic body is false, like the one found on the 60D. Yuck! If it has a metal body like the 5D2 or 7D, I would have to consider buying one. 
D
Don't you like a REBEL FULL FRAME? 
A Rebel Full Frame is the way for Canon to go at some point, but that all depends on when the cost of producing FF sensors comes down vs the EF-S lens market the rebels have. I can't see Canon selling an FF body at a loss in the hope of recouping the money by way of lens purchases and other accessories. Nikon can only really offer the D600 at that price because it's getting the sensors via Sony and scrimping everywhere else. Canon is in the same boat in a way, it has the sensors and the technology to produce a budget FF camera whenever they like. I tend to think they have been waiting for Nikon to pull the trigger on the D600 before they respond. Canon loves to steal Nikon's thunder quite often or at least the PR peeps do.
As for me ? I'll be sticking with Canon. While they do need to update the sensor technology (who really knows what's going in Canon's R&D departments), it's not that bad really. My 50D coupled with my L lenses produces some very good images. I do have an upgrade itch, but I'm waiting to see how Canon responds to Nikon before I take the plunge.
If there is a budget FF camera from Canon, It won't surprise me if it's got a similar body construction to that of the 60D. If the plastic's good enough for glocks...