I am finding frustration when shooting in dim churches and the bride or groom are moving around. Some motion blur is ok if most of the subject is sharp. With my D300 I find that ISO 1600 sometimes is necessary but not satisfactory. I shoot raw but find that if I need to adjust the exposure in my raw converter, the noise jumps out. I would love to try a D700 to see if its sensitivity in dim light is truly as good as users say. Of course, getting one would necessitate one or two full frame (FX) lenses. I'm a bit geeked though after comparing sensor characteristics on dxomark.com. The Nikon FX sensor looks to be the best in the industry at this time.
The issue of not using my DX lenses on my D300 can be avoided by just keeping my 18-200 on it full time. That lens is just too good and versatile to not use. I have used it extensively at a local race track for the past year and, when the light is good, I get sharp shots even when printed to 20x30 (after shrinking the image files to under 5MB so I can use my local cheapy Sam's Club).
Here's a Nikon pet peeve. Why won't Nikon produce a nice midrange zoom like Canon's 24-105 with a constant aperture? That lens is very successful for Canon and I never found it to be too large or heavy. Nikon just seems to be fixated on the f3.5-5.6 aperture range. Hey Nikon, not everyone shoots with full automation!

Christopher--Yes, that is the rub. The smaller sensors just don't have it at high ISOs and the larger sensors require "full-frame" lenses.

Good question about Nikon mid-range zooms. My two favorite reasonably priced mid-range zooms for my D700 are the Sigma 24-70 f/2.8 (7 oz. lighter and half the price of the Nikon version--not quite as amazing image wise, but smaller & lighter & cheaper) and my (somewhat old now) 24-85 f/2.8-f4 with Macro, which is quick & I have found it sharp (although some reviewers disagree). Note that this is not the AF-S version (which I also have), but the AF-S version is slower as far as aperture and subjectively I don't have the same confidence in its sharpness.

Either way you will be impressed by the improvement in high ISO from the D300 to the D700. I can only imagine what an eventual D700S (with the D3S sensor) might be like when it eventually comes out. --David

Ricky: Thanks for the insight. I will make a a point of clicking through if I order from Amazon or B&H.

Well, after much reading, and research, I ordered the D700. Should have it in the next couple days. Thanks for the input here. I'll try to come back with my thoughts.

Andy--I suspect you'll love it!--David

I buy most of my gear from B&H and Amazon too. They are great to deal with.
Like what Rick said, please use those click-throughs when you buy your photographic gear. I have a D200 and D300 as well and although they are DX cameras, I am still enjoying my FX NIkon 14-24 and 24-70 lens on both of my DX cameras. These lens are sharp, sharp, sharp. I am getting ready to move up to full frame cameras too, like the D3S so that I can take the full advantage of both the nano crystal coated 14-24 and 24-70 FX lenses.

effie