okay, lr2 is for mass editiing. if you were doing a wedding, especially with digital, it is a real time saver. lr2 is more of a batch editor, although lr2 is a huge leap forward over lr. i have yet to try lr3. i just edited four seperate commercial jobs over the last week, and without lr2 or a similar programme, it would have added maybe 1000% post time using cs4 or similar. but for single images, maybe to prepare for a print, or to do some major editing on, there is no subsititute for photoshop.
another common issue with digital, is dust on the sensor. if you were to take 500 images with an annoying spot on them, a programme like lr2 can assist in removing it quickly to the batch.