Please don't bring FCPX into this. The updates have fixed pretty much everything that was missing before. Anything missing now is either people moaning on the littlest thing or they just don't want to relearn the future of editors. FCPX is a complete break from previous NLE's and until ppl understand that, they will continue to not get it. So with that, now to Mac Pro's... there are more than enough solutions out there that work wonders as HenryDJP has so elegantly stated (Henry I +1 you on that post).
Now with that set aside, I'm very happy with LR4. I was thinking about waiting for Ap4, but I used a trial of LR4 and it felt like being right at home. Things are setup just the way I want them to. Will I upgrade to LR5? Probably not. Why? Because I really just use it for organizational purposes. I'm just a guy with a DSLR that takes photos here and there, not much of a color correction or anything like that. So for photo management, I'm very pleased with LR4.
For those of you who are thinking about Lightroom, I say take the dive! Grab the beta and hold out till LR5 is released and buy it. If your doing photo management, LR4 will fit the bill, you could even wait till LR5 and get a deal on LR4.