I really can't answer your question directly as this is my first Nikon DSLR. I have been using my D700 to take 100 or so images with lots of checking things out on the LCD plus lots of use of the menu to change/adjust setting and it is still on the same battery and initial charge. That is good enough for me but how it compares to other models I don't know. I am sure that if there was any glaring deficiency in battery life, or any other deficiency for that matter, you would have heard about it by now.
Nikon gives figues for expected battery life in the camera manuals. Whilst these are not really a great guide to how long a battery might last for any given user, they are done using a standard test procedure and thus should allow a reasonable comparison of battery performance in different cameras.
For example, with one EN-EL3e in the camera, the approximate estimates given are:
D700 - 2,500 D300 - 3,000 D200 - 1,800
So I would expect the D700 battery life to be noticeably better than the D200, but not as good as the D300.
This is very subjective, but it seems to me that my D700 is going through the battery much more quickly than my D300. But, I haven't tested it in any systematic way, so it is possible that I am wrong.I would be interested to know if anyone else has measured batter life.
I'm using mine with the MB-D10 attached a battery borrowed from my D2x. After 155 photos (and lots of chimping) I have 99% left in the in camera battery and 84% in the EN-EL4a battery. I love that you can see battery info for both batteries!
I previously used the D200 and I have only used my new D700 on a few occasions but the one thing I did notice was the battery life is very much improved. I also have the MB-D10 grip with an extra cell and on two full days shooting at the Edinburgh Fringe I have only exhausted one battery. Previously with my D200 I would have to charge both cells for the second day's shooting and even occasionaly have to use AA cells towards the end of the day.
I never ran the battery all the down in my D200 or D300, and I don't do so in the D700 or D3 either. The charge/recharge cycles of these particular sorts of batteries seem to respond better with only occassional full drains (especially using the fancy-schmancy charger supplied with the D3). So far, the EN-EL3e in the D700 is running for days (and at least 1,500 exposures) before I get down to somewhere between 25%-50% of charge capacity, at which point I switch to a spare EN-EL3e and recharge the other one.
The first full charge seemed to last as long (see above) as it did for similar use in my D300. I think the second charge has lasted longer (going strictly by exposure count) but it's kind of meaningless/impossible to estimate in that I have no real way of accurately matching shots, fill flash usage and so on with previous usage of another camera and battery combination.
My subjective impressions are that the electronics in the D700 are incrementally more efficient than in previous bodies in this form factor and that battery life is consequently slightly longer per charge. Considering that battery life in the D200 and D300 was/is excellent, it's good news all around.