Not sure if package changes are appropriate for this thread but
Sky Arts 1, Sky Arts 2 (the SD versions) and Yesterday +1 have been added to the M+ tier.
I noticed the additions when I was messing about with the Set Favourite Channels menu last night and have confirmed the change on the Virgin Channel listing website where they are all now ticked in the M+ column.
http://shop.virginmedia.com/digital-tv/channels.html