Just edited my first session with the full LR3, having used the beta on and off for the last few months.
Wow!!!, is all I can say.
A few points:
1. The new rendering engine is terrific. One of the big knocks against LR in the past has been that Adobe's RAW rendering was not super accurate. Well, the new engine seems to be a lot closer to what I would call "accurate"; nothing scientific at this point, but it seems really nice, though it does take a bit longer to render previews.
2. Noise reduction is unreal. Seriously, this is as good as I need, and I don't anticipate having to bring out Noiseware anymore.
3. Overall speed (with the exception of RAW rendering using the new engine) is MUCH better than v2.7 on my Penryn MBP.
4. Grain simulation is a nice touch, and works beautifully with many of the Presetopia presets I use.
5. Built-in lens correction. Wow!
6. Sharpening seems to be much nicer too; not sure how to describe it, but I seem to be able to get more aggressive with sharpening without causing as many nasties.
With the new watermarking tools, the improved sharpening, and the incredible noise reduction, I'm sure that my need for Photoshop will become next to zero; the only thing I will need PS for is layer masking, and I already did less of that since adjustment brushes were introduced in v2.0.
LR3 is a seriously awesome program!