I have looked at the comparison between the D3 and D700 since they came out and I think I am going with the D700, and I really have a choice between either.
I went into my local Nikon dealer yesterday and they had a D3 for me to play around with and I asked them about going between the two and they just didn't know, not until they got one in their hands (they are getting 4 total on Aug 1).
What I found is and my running total of pluses and minuses (course this is purely subjective):
1. D700 has a self cleaning sensor unit, D3 does not (to me, needed) <+1 D700>
2. D3 has dual CF slots, D700 does not (that is a cool feature) <+1 D3>
3. D700 has monitor screen cover, D3 no (no biggie) <+0.5 D700>
4. D3 has 100% viewfinder coverage, D700 has 95% (probably the biggest negative about the D700 to me, but I understand why) <+2 D3>
5. D3 has 9-fps vs D300 8-fps (assuming grip, no biggie here, one single frame per second) <+0.5 D3>
6. Shutter durability D3 300k vs D700 150k (never made it that high before trading a body in) <+1 D3>
7. Voice memo on D3, none on D700 (to me, who cares) <+/- 0>
8. Battery grip D3 built in, D700 buy (I love the built in grip) <+1 D3>
9. Weight, D700 995g, D3 1,240g (for those of us in the U.S. who are mentally challenged at anything other than pounds, D700 just over 2 pounds, D3 just under 3 pounds, good difference) <+1.5 D700>
10. Price D3-$5k, D700-$3k (big difference to me, if I go with the D700 I can get at least the 14-24 or 70-200 and still have change, so we are basically talking about extra glass, and really good glass at that) <+2.5 D300>
11. Release Date / Asset value, D3-Aug 2007, D700-Aug 2008 (to me, constantly upgrade is a pain and expensive, I put this in there just because the D700 theoretically buys me a year of new development. When is the D4 out, January, June 09, September 09, who knows, but as soon as I buy it, it is sure to be on the way) <+2 D700>
There were very minor differences not mentioned here because, to me, they didn't make a difference in my purchase decision.
So, if you add up all the pluses and minuses you get <+1 D700>. It could go either way as the above is subjective. If I drop #11, the D3 has it by +1, so this is just my take on it.
I think I will probably take one of the 4 my local dealer gets and use both my D300/D700 combo. Now, if the new 70-200mm would just come out with the "N" coating that would be great (and make it more impossible to get).