CS3 is going to be a new concept in a lot of ways with the different levels of functionality. Familiar to CS2 based on the beta, but with the different add-ons for different specialized uses, it will be undoubtedly a much larger package to use and learn.

Lightroom is a whole new concept and looks like it is going to be a great workflow tool. I've been using it for a while now. It doesn't replace Adobe Photoshop CS2 or any of the other tools, it just takes the parts that photographer's seem to use the most and puts them in one package. Since it is presented as 'modular' the hope is that new module will become available for various upgrades and enhancements as time progresses.

Nikon Capture, and I've only played with it briefly, is still more of the proprietary type of tool. For .NEF conversions though, it does seem to be preferred by many Nikon shooters. Then again, I haven't heard much feedback yet on it vs. either Lightroom or the CS3 beta.

I would offer this, if you are initially looking at working with lots of images, both existent and are going to be shooting a lot in the upcoming few months, go for Lightroom.

If you have very specific, production and editing needs, wait for CS3. With Lightroom you could always use a copy of Elements or another editor as well and still not be in the cost range of the full blown editing suite.