LR is out of beta and final release is now available at http://www.adobe.com
The betas will work until 3/31/12.
The US price has dropped to $149.00 for a new user (might change eventually) and $79.00 for an upgrade from I belief all earlier versions but definitely for LR-3.
From my beta experiences I feel LR-4 is a very significant and useful upgrade over LR-3. I would certainly recommend it.
UPDATE: Windows XP users see Pavel's important message below. Thank's T-Lama