As usual I'm a little late to the party here. I generally recommend Lightroom as a great solution for most people, but I personally don't like it as I find it generally lacking.
On the whole I am very impressed with CS4 and I have to say that this version of Bridge doesn't suck, or at least not as much as previous versions, and I have been using it for general DAM stuff.
What makes LR great is that it is an all in one ingest, metadata, process and DAM solution. However, I don't find it all that great at any of them though IMO it has the best and cleanest workflow. For raw conversion I much prefer the output of Capture One, though I don't love the interface or workflow it forces.
DAM is still an area I don't know where to go. I really liked iView3, but I don't have faith in Microsoft developing it further. I don't like the way that Adobe handles DAM, but I believe they are committed. Hence my dilemma.
To answer your question, I consider CS4 necessary and LR2 nice if you decide you want it. I'm pretty sure that anything you can do in LR you can do in CS4.
