The public Beta has been out for a while, but this is the official update. Basically it adds camera support, but I always install these official releases as they usually tweak some things under the hood.
From Adobe:
• Additional camera support for the Canon 50D, Canon 1000D (Digital Rebel XS/EOS Kiss F), Nikon D700, Nikon D90, Sony A900, and more
• Several corrections for issues introduced by the Lightroom 2 release
Link to Windows Download Link to MAC Download
And if you have not bought Lightroom 2 yet…why? Go directly to Amazon via this link and buy it!
Adobe Photoshop Lightroom 2
Adobe Photoshop Lightroom 2 Upgrade
