I myself am one who does not follow the pack on why not spend 3000 on an A900 instead of the D3x. They are truly different cameras just like the argument many pros who are mad at Canon on the 5DMKII vs 1DsMKIII debate.
The D3x has these features that are alone worth a hefty price tag vs the A900 and 5DMKII:
Weathering sealing with weather sealed lenses because one the 5DMKII is not weather sealed and the A900 is but Sony won't tell me which lens they have is weather sealed.
An advanced AF system... the clunky 9pt single cross type AF system in the 5DMKII and A900 are blown away by the Nikons 51pt AF which has now been rated as the fastest lowlight AF system and that matters a lot to pro shooting weddings, sports, etc.
Noise... if we look at ISO 400 and above the D3X blows the A900 just completely out of the water. Heavy handed noise reduction and large blotches plague the Sony system since the advent of the A700, while the Canon rides smoothly along with the D3X until we hit above 2000 where the D3x is able to retain much more detail. Canon always uses heavy noise reduction which smudges all useable detail away.
Metering... well I know Sony has decent metering and so does Canon, but Nikon definitely wins in the metering and WB camp with their full frame cameras. Some reason the A900 I have shot with can't hold it's metering, either over or underexposed with no regular pattern. Canon always seems a little hot to me at times with the 5DMKII and the dynamic range is pretty poor with the camera so highlight clipping is just something you'll deal with.
Buffer... so the Canon can do 12 raw photos, Sony does 13 raw files and the D3x doesn't have a firm raw buffer but I'm taking a stab at 18 RAW which at it's file sizes just blows the other two out of the water for pro shooting. The dual CF slots also help a lot and yes I know with Sony I can put a MS pro duo in there, but I don't want two memory card formats to play with.
Live view... I hate the thing myself but Nikon wins in AF speed in live view AF using contrast detect. But the Canon wins cause it takes video??? Not my cup of tea but a def use for certain photographers.
Image potential.. with a 100+MB raw file you can loads of editing to and retain tons of detail while manipulating it. Just that is a big draw that neither of the competition can handle.
If we dig deep the shutter lag and response times are twice as fast in the D3x vs the competition.
Battery performance... the Nikon battery system dwarfs the competition here with it's massive EnEl4a battery. Even with a grip neither Canon nor Sony can take the same number of shots.
Noise... yes again I just have to mention how bad the A900 noise is again because it just stinks!
For the price you get more but that is again for a price. If I had the cash, and I do, I wouldn't buy one cause I can get the same camera in a D700 and get two great f2.8 lenses and a grip with an ENEL4a.
I still think the D3x is worth the bucks, cause if it isn't than the 1DsMKIII isn't worth the buck either. It's not a just the same A900 sensor in a Nikon body, Nikon actually made good use of it.
BTW, Pentax, if you can hear me I'd like a FF 18MP for Christmas