Thought I'd add something here, as I've been using MB for a while and think it's such a cool app.
Anyway, I have DVD's ripped to a media server in there native VIDEO_TS/VOB format, which VMC plays fine. I also have HD movies ripped to MKV format in another location, which means I keep DVD's and HD movies in seperate root folders. I created .vf's for each folder that MB can use, with a graphic saying 'DVD Movies' and 'HD Movies' on the frontend, so I know which are which. I'm using standard movie poster images for each film (not BD covers, or Photoshop creations), and it works fine. The icing on the cake is to use the mediainfo trick in MB, so the format of the HD .mkv file is detected, and I automatically get an icon displayed in the bottom right corner of the poster image saying 'HD 1080P' or HD 720P' depending on the format. I don't have to change anything, or mess around in Photoshop.
I'm happy with this, as it works really well with no other work required.
I've also registered the MPC-HC video decoder in VMC, so I can playback 1080P mkv's WITHIN VMC with full acceleration. This works ok, although I'm really waiting for MB to allow 3rd party apps (such as MPC-HC) to automatically load and play the mkv file. This should be coming soon.