Lightroom 4 is now shipping. The best new feature: the new price :D
I'm a relatively new user of Lightroom (having used it only a year and a half) but I have since found it to be an absolutely essential software. Without Lightroom, my workflow would be much more tedious and would take perhaps five times longer. (Intro to Lightroom 3).
I downloaded the Lightroom 4 beta, and a lot of people say it's a major upgrade, but in my opinion it's not such a huge upgrade from Lightroom 3. That said, I found the new controls to be much more sensible and easy to use. I also like the slight improvement in image quality. Because I use Lightroom so much, upgrading was a no-brainer for me.
As soon as I found out about the Lightroom 4 release, I ordered it. I was pleasantly surprised at the price drop. I always thought that Lightroom was overpriced for such simple (albeit essential) software. At this new price, it would be a crime not to use it.
Lightroom 4 is currently out of stock at most major retailers but it's possible to download it directly from Adobe.
BTW when I tried the beta I found it somewhat slow and it crashed frequently. At least one user of the release version has said it performs better. I am still downloading it as we speak (not surprisingly Adobe's servers are pretty slow now) and will post about that when I install it.
UPDATE: I've installed Lightroom 4 and I would say that the performance is indeed much better (on my slow laptop) compared to that of the beta. I haven't experienced any crashes, though sometimes it seems to load for a while. I also tried changing the process version for 630 photos, which didn't take long but after the change, whenever I tried to bring up a photo, it seems like would have to create a new preview, which may make the computer seem like it's freezing up when it's actually hard at work.
The upgrade was also relatively painless. It seems my presets, camera profiles, etc. were carried over, with the exception of one publishing preset (jf Picasaweb) which I need to download again. BTW, some users such as Neil van Niekerk have experienced problems receiving the serial number. In my case, I received my serial number by email around 3pm after ordering LR4 around 830am.