Easy browse network shares (window and linux shares) and play .mp3 content, be able to add big .mp3 collections (big as in 5TB+ range..) without the mediacenter choking trying to collect info and choking when trying to browse the colletion. Be able to play x264 content in .mkv container, be able to play divx/xvid, show photos in .jpg. When it comes to movies and tv-shows, the possibility to browse based on folders and if a .rar collection of files (.r01 .r02 ... .rar) and the mediacenter would unrar file by file as needed and play back the content, and if the content being a .iso .img file etc, automount it up and show it as a dvd movie (as most .iso etc is dvd-rips).
So, am I even remotely close if I go with Linux MCE? or should I wait for XBMC's linux port, as these things works out of the box on a xbox, but the limit is the hardware so no 720p x264 stuff :/