Although the 300s is comparable to the D700. Both the D700 and the D90 exceed what the D300 can do in many catagories

I got a D300 the summer following the launch and absolutely loved what I got out of the camera. Now I shoot on a D700 and have a D300s for backup, video and reach I supposed. But to be perfectly honest I haven't shot a single day of wildlife with the D300s since I got the pair of bodies. I shoot wildlife pretty much only with my 300mm and the extra reach just hasn't proven to be that useful to me yet. The ISO capabilities of the D700 and its IQ just make for way nicer results and way less missed opportunities. My only complaint is the 5fps vs. 7fps. That being said, I expect that when I can afford the 300mm 2.8 VR that I will then slap my TC-E onto the D300s and finally be able to use the auto focus whilst shooting at 900mm. Only then do I think that I will value its extra reach.

one more thing about using D700 with battery grip - if You shoot mostly with grip attached You can check the price of used D3, as it may be comparable to the price of new D700 + grip + new battery and charger (if You are really into the FPS), also D3 is little bit smaller than D700 with MB-D10.

I use both D700 and D300 for different purposes of course. If finance is tight, I would go for D300. Otherwise, you need to have both FX and DX. Because DX can give the long reach that FX lenses couldn't provide at the same focal length.

I'm strongly in the D700 camp. I like to do lots of low-light stuff, and would kill to have a D700's high ISO performance. In a perfect world, I'd use a D700 as my primary body, and a D90 or D300 fitted with a tele-zoom as my secondary camera.

The D300 has a 100% viewfinder as Adamz said above. Don't discount that... its important for composition. I hate it when I'm shooting with my D40 (90% viewfinder) and I always wind up with more picture than I intended. I just crop it, but with only 6 MP to work with, it can be a real pain. The viewfinder on the D700 is 96%, which is much better, but still not 100%. The gotcha is that you are seeing 96% of a larger sensor, so you can see your image a little more clearly... just not all of it (of course you get 100% coverage in DX crop mode). Your shooting style will dictate what works best here.

I've shot with both, in fact I traded down from a D700 to a D300 for several months... I felt the D700 and lenses were too heavy for what I wanted. Worst mistake I've made in a long time. I hated it. The image quality is nothing like the D700. So after a few months I repurchased a D700. The good news is the D700 held it's value very well when I sold it 6 month ago on Craigs List and had come down in price at retail a little by the time I replaced it (last month).

IMHO, the is no question... the D700 is a much much better body, and a given the D300's age a better value too. When the D400 comes out I might be convinced the D400 could provide a better "value", but not the D300. If your really looking for value get a D40x or D90.

I'm not being a snob, I've truely shot with both extensively, but having gone to FX and then back to DX I was constantly disappointed with the IQ and lens choices available. If you only plan on shooting with consumer grade super-zooms (18-200 VR) then maybe a D300 would make sense, but then I'd think the D90 is really a better choice. I notice only very slight IQ difference between my old D80 and my D300, whereas the difference with the D700 is very noticeable. Until Nikon get serious and starts making pro lenses (f/2.8 w/ good glass) for DX I'm no longer going to take the DX line seriously either.

if you question is 'value for money' d300 is much better
however if you pay extra you get that ISO that everyone is talking about + speed + full frame (at this stage Isee it more as a down side for nikons since there is not enough lenses hehe)
but you also get this extra few grams and size increase

if you looking for simple answer yes\no ... no one will give you one its for you to decide based on a requirements that you look for in a camera

newfie - as for fps, once You add grip the speed is the same

mb - I will disagree with You, that You can use lower quality lenses on D700, as than You are loosing the potential of a FX frame.

gentoo - finally we can agree on one topic :) - if You shoot wildlife go for d300 (or any DXXX) if You don't need the extra reach go for D700 (better iso)

one more factor is the wiefinder, on one hand D700 is better as it's simply bigger, OTOH it's only 96% coverage, while D300 has a 100% coverage (this what You see in the VF is exactly the same as You see on the picture

They each have their advantages. The D700 of course has the low light advantage, which is huge. The extra reach on the D300 combined with the coverage by the AF system of the full frame makes it the better of the two for birding, sports, or most applications where you're using longer focal lengths.

I agree that both cameras are structurally almost identical but the D700 is heavier camera to use because you need the larger FX lenses if you want to get the most out of the camera. In terms of build quality, the D700 is slightly better, most notably with respect to weather sealing.

The build quality is actually the same.
Image quality is also the same in average conditions and good quality DX glass on D300; if you compare pictures of the same size pixel by pixel they are almost identical (I have not been able to notice any significant difference, almost as if they were shot with the same camera).
Low light is different story, D700 is much better at higher ISO.
There is one more thing; you could actually use lower quality lenses on D700 because of it larger sensor, Nikon AF-S VR ED 70-300mm f/4.5-5.6G IF for example will give you great results for sports

This really depends on what you shoot. If you do landscapes and a lot of low light stuff, the D700 was a good choice. If you do wildlife like I do, the crop factor is a blessing and a gift. Size wize, the D300 is only marginally smaller than the D700: http://www.kenrockwell.com/nikon/d700/D3S_9000-1200.jpg Weight wize, I can't notice any difference but, I'm not the best to judge weight because to a guy who lifts weights like I do, all camera gear is light lol.

To answer your question, I don't think one is really superior to the other. I normally hate this answer but in this case, I think I can say that it's a matter of preference and what and how you shoot.

I think that the differences in weight and size are really negligible.
I had a quick side-by-side look at them (dpreview) and apart from the sensor size, there aren't really that many technical differences.
The question here is whether you need the FX sensor or not.

I currently use the D700 but as of late I am wondering if the D300 might actually be the better camera. Except for ISO performance and build quality I/m beginning to believe that the D300 is a much better value. Slightly smaller and lighter, cheaper, uses DX lenses (again lighter and cheaper) faster frame rate .....etc. If Nikon put some serious effort into designing 2.8 (or faster) pro quality lenses, the D300 might just be the camera of choice for more serious amateurs and pros. Don't get me wrong, I love my D700 but is it really a superior camera to the D300? I have my doubts.