Having studied the specs of the Canon 600D and finally had a chance to use the camera over the last 24 hours I have to say that it is probably the best value for money camera vs specification that Canon currently have in their lineup.
So far I can only see one reason why you would want the Canon 7D instead of the Canon 600D and that is the faster frame rate. Unless you are shooting sports or are particularly clumsy and drop cameras I can see no benefit in the Canon 7D compared to the 600D.
In fact the Canon 600D has a lot of features that would be very useful on the Canon 5D MarkII, the rotating screen, video crop mode, flash control in camera and additional "small JPG" S1/S2/S3 options will undoubtedly be in the Canon 5D3 spec sheet.
