It's been a long time in coming but the beta version of XBMC 11 has now been released. Version 11 "Eden" adds lots of new features and improvements to the open source home theater software for both Mac and Windows.
There are also significant speed increases thanks to what's known as "Dirty-region rendering", a new JPEG decoder, a simpler, better library, additional protocol handling, better networking support, better handling of unencrypted BluRay content and structures, adjustable display refresh rates in OSX (to match the already available feature in Windows and Linux), AirPlay support, an upgraded weather service, and much more.
You can find details of all the new additions and changes to XBMC in the changelog.
Although not finished yet, there are also important changes in progress to XBMC Live to make it more like a full “*Buntu” version of XBMC with major changes to the boot and install process.