Besides what was said above, Thom Hogan in his recent (& late!) D3 review mentions: - Pro D700 Difference: Gridlines in viewfinder, Focus Assist lamp, Better Info screen handling & LCD protective cover supplied - Pro D3 Difference: Better weather sealing, Extra secondary LCD on back, Smaller size when grip is used on both
I think he nails it with "D700 is more targeted to the serious amateur and pro backup market".
Lack of portability & hefty price is what ruled out the D3 for my type of photography & budget & is what makes the D700 so attractive to me.
Built-in flash & sensor cleaning module are quite useful in a pinch when you want the smallest possible package when hiking or shooting in a crowd.
Since the engine is the same (sensor), cup holders, interior trimmings & mp3 connector differences are really not that important for me.
In the field self sensor cleaning with a D300 in 15 seconds through menu (vs. D3 lens off, mirror locked-up & blower):