Download Adobe Photoshop Lightroom 4.1 Release Candidate - Adobe Labs
This is a release candidate only - so is not a final version.
It adds a few cameras and corrects a few bugs and other issues.
The best thing for me is that it adds back manual CA adjustment sliders - nagging Adobe (as I and a few others have) really can make a difference!
It is not noted as specifically addressing performance issues, which remain significant in RC1, unfortunately for many users (myself very much included)
I'll download this tomorrow when I have a bit more bandwiidth available.