Adobe Lightroom 2.2 is mainly a bug fix release with additional camera support.
New cameras: Canon 5D MkII, Powershot G10, Panasonic DMC-G1, DMC-FX150, DMC-FZ28, DMC-LX3, Leica D-LUX 4.
If you use one of the Panasonic or Leica cameras noted above, and you usually use the DNG format, do check the readme for further details.
The new color profiles will be installed, if you haven’t done so already, and it now defaults to the new Adobe Standard profile rather than the old ACR 4.4 matrix profile.
There’s a list of bug fixes in the readme file, but particularly notable are the improvements to the performance of the Adjustment Brush and Graduated Filter, which is improving with each release.