Had this thought today... Something about the form factor of the current TBD irks me considering the iMac 27" is currently a thinner design. Can't help but thinking using Target Display Mode is a really nice option, combining two computers into one, with Command F2 making it really easy to switch between the two machines. You could get the base iMac 27", use the Mac Pro predominantly with the iMac in display mode, then, say if you were rendering or putting out some compute heavy task, just Command F2 and switch to the iMac, keep working (or come up with a whole range of reasons to work between two computers in this way). In lieu of Apple releasing a new form factor Thunderbolt Display it's an option, I guess, although a slightly more expensive one. And in a funny way it's a way to squeeze a 21.5" display out of Apple also, even though they don't currently offer one. At least if a new display comes out you'll be able to sell the iMac for a decent price and upgrade, whereas the TB display may depreciate quite rapidly.