I was excited to download and try LR/4 but completely disappointed that it won't load or run under Window's XP. The error message says that I need Vista or later. The very last thing I would ever to is to "upgrade" to Vista. Adobe, get real! Yes, Windows 7 is out there and no, most people have not adopted it as an OS. WinXP-Pro is very stable, fast and robust and unless there is some compelling reason to upgrade to Win7 (such as needing to run AutoCad in 64 bit mode), it just isn't worth it. I guess I will be using Lightroom 3.x for a long time because Win/7 isn't going to happen in this office in the forseeable future.
I would have to report that Lightroom 4.beta is one big bug that needs a basic fixing.