Hmm. You can't use a previous catalogue. In that case it's really just for testing, I'm not starting again...
When friends or clients post comments and ratings on your Flickr galleries, you can immediately see their feedback in the Lightroom 3 Library alongside your image
Noise reduction and improved RAW algorithms seem good. If the final version has correction for barrel/ pincushion distortion and soft proofing I'll be happily handing over hard cash.