The latest MPlayer code in their Subversion repository now supports most Blu-ray and HD-DVD codecs. MPlayer though cannot play any content "out of the box", but there is an MPlayer patch on the Doom9 Forums that provides a library and patch to be applied against the latest SVN code that drops in Blu-ray playback support. There is also support for ripping legal copies of Blu-ray content on Linux using this guide.
Finally it's becoming possible to play your legal Blu-ray movies on Linux. More details on the MPlayer web-site.