I had a similar choice, wanting to upgrade my D200 for better high ISO shooting, as well as gaining liveview for macros and such. I'm not tempted by FX as I like to shoot wildlife and enjoy the reach of DX. I chose the D7K over the D300s as the draw of new technology won me over vs. the more familiar build and ergonomics of the D300s.
After two evenings of shooting, I'm quite impressed with the performance of the D7K. I just updated my LR3 ISO Presets and just marvel at the quality of ISO1600+ (coming from my D200). Happily, the lower ISO images are wonderfully detailed. I need to relearn a few button positions, but that's pretty easy. Reaching for AF-On(AEL) is a bit awkward as I am left-eye dominant, but can be readily accomodated.
I assume the AF performance will be better than what I have now, but will not match the higher-end bodies. Overall, I see no significant drawbacks with this camera for my use.