I'm replying about Canon RAW formats (also for other brand camera RAW)

Canon latest camera 40D and 450D raw are saved with .cr2 however it's different compression make them unreadable until update.

Since Xee depending on OSX Raw support. You can download the "Digital Camera RAW Support update" from apple website.

So RAW problem is not there because of Xee but because camera developer keep making new format and using same extention