Well actually, I have an advance copy of Martin's Lightroom 2 Book and I have read through it...it's quite advanced over the previous book (about 625 pages for the new book and 350 pages for the 1.0 book) and the material in the 2.0 book is pretty much a total rewrite...so I would be inclined to suggest this book (note: I have NOT read Scott's yet and Martin is a friend).
Course, if you want to learn LR 2, you might also consider Mike and my LR 2 video tutorial...
I'm pretty much non-biased (don't know any of them LOL), but--I do have Martin's first book and really like it--and plan to buy his 2.0 book as a reference.
However, I became a convert to LR from the first LL video series (after getting LR free as an RSP licensee and having tried the beta but drifted back to PS when PSCS3 came out).
I first watched the Camera to Print series--and noticed how much Michael and Jeff used LR and it made me reconsider LR. So---I bought the REALLY reasonably priced LR 1.0 series and became an LR convert (moved from another database, etc. to LR).
I dled the 2.0 beta but admittedly didn't spend as much time with it as I had hoped, so wasn't really 'up' on the new features. I've now watched the videos through the 'calibration in Develop module' video and have a MUCH better grasp of all that's new (and can say that a newbie to Lightroom will 'get it' also) and can highy recommend it. The video on the filters in Library module were just excellent as well as the new features in the Develop module (very well demoed). I also loved the calibration video explaining the new profiles and dng editor and just downloaded and installed the profiles (wow). I had read about them yesterday but was still unclear about how to actually use them or get them--but that's all explained and much much more. Worth every penny IMO.
I was using LR about 80/20 but wonder now if that will increase quite a bit with the new features.