I know it is not that 'obvious' because it works mostly behind the scenes, but I think it is a huge benefit to know if plugins and skins you have installed are compatible with your current version of MP! And now even MPEI and the Extensions plugin tell you if they aren't before you even install an incompatible version.
I would like to see a harder handling of plugin. Today there are to many ways to Rome. Because I have seen people not caring about adding their plugin to the MP site... or any other place liked to MP. So a harder restriction of installing of plugin's like only trough Extension would I like to see in 2012...
I'd vote for MyFilms (awesome being able to browse my entire movie database in MP) and PureVisionHD Blue (love the way the menus are presented in subsections on the Home screen, compared to the endless vertical scrolling list used in Default and StreamedMP). Although I'd probably agree that MPEI is no. 1
Since I already ran a stable MediaPortal setup in 2010 and before, I limited my votes to the major impacts for 2011 that I went through.
So eventhough I was using MPEI before, in 2011 it really took off to become the 'to go' method to expand things and more importantly to keep it all up-to-date when MediaPortal v1.2.x came into light.
The Extensions plugin really makes that easy from a couch perspective, which for a HTPC is the place to be
And finally hyperlink support, because of a feature that I wanted for MP-TVSeries to bypass my PIN-code protected views, and indirectly via trailer support inside Moving-Pictures plugin.
Would have voted for my own IMDb+ if it was on there, because it has occupied a large part of 2011 for me, but it is a fun experience that is rewarding enough by itself.
PS: Only got around to mvCentral today, so that will have to be my vote for 2012
Personally, I really don't care about graphics, skins, coverart, fanart and all other optical eye-candy's...
For me stability, functionality, performance and usability are the main-points which should be improved primarily.