I decided to try out a 5dII mainly because I'm interested in doing some larger prints (maybe up to 20x30), and I've been comparing it to my 7D for a couple of weeks.
Probably the biggest difference I've noticed is the additional "depth" of the data files for the 5DII. There's noticeably more latitude for cropping, editing, noise reduction, etc. before running out of resolution or noise becoming too obvious. The 7D is still quite good though; I'd say (subjectively) 80-90% of the 5DII.
I only plan to keep one of the bodies (too much $ for a hobby to keep both, or for a 5DIII), and I'm leaning towards keeping the 7D. The 5DII does have better image quality IMO, but I'm not convinced it's enough of a difference for me.
Another big factor in favor of the 7D is that I've got some nice crop-only lenses that would be hard to part with. Plus, I just like using the 7D better than the 5DII, mostly because of the autofocus but some other features are nice (level display, customization options).
Anyway, I do need to spend a little more time with both bodies. Whatever I decide it's been fun to try out some different equipment, which is just part of the fun of this hobby.
7D2 - Samyang 14mm - Sigma 17-70 - Sigma 50mm f/1.4 - Canon 40mm - Tokina 50-135 - Canon 70-200 f/4 (non-IS) - Canon 300mm f/4 IS - Canon 100-400 v.1 - Canon 1.4x TC - Kenko 1.4x TC