By the way the 5D2 is not the perfect fit for me, I'd really like better AF and a fix for the intermittent banding issues. I just mention the 5D2 because it's the one to beat in the price range. And it's killing the competition in terms of sales ( according to the sales dudes in NYC pro camera shops.)
Doh, sorry to be presumptive. I should have asked more questions first. It doesn't surprise me that the 5Dii is selling so well. There was a gigantic 5D user base to begin with, and the D700 is a year old. Sony never really had a chance to compete in that regard. Plus, in my daily non-camera-forum-geek life, the issues of the 5dii (like banding,) are largely unknown, and it is a great camera. I don't think the A900's AF would be good enough to warrant a switch from the 5Dii. If you can deal with no video, the 1Dsiii or D3x may be the better choice (or D700 if you don't need the resolution.)
I would characterize the my time with the A900 (and I guess the A850) like this:
-Wonderful low ISO (100-400), good mid ISO (625-1250), acceptable high ISO (1600-3200)
-great (maybe the best) center point AF, pedestrian outside points/tracking
-Outrageous viewfinder that is big and bright (A850 supposedly looks near-identical, even though it is only 98%)
-Average battery life
-Huge file sizes (36MB RAWs)
-Flash system better than Canon, worse than Nikon (but I'm not the best authority here)
-two memory cards is nice, but no auto-switching is ridiculous
-best vertical grip of any camera made (although a bit ugly)
-non-standard flash shoe is slightly annoying, but it has its strengths, too
-AF Zeiss lenses are incredible.
-I love shooting stabilized below 100mm
-I actually like the uncluttered, big numbered top LCD, but I'm in the minority
-The feel, handling, and overall "vibe" of this camera is unlike anything I've used in a while. Uh oh, could this be love? lol.