the Music store is decent. easy to get to, relatively easy to navigate, a bit sparse right now since it is just a beta.
sparse in both features and selection.
60 second song previews, .77 cents per song. the Ubuntu people partnered with 7digital for the store. the store is integrated into Rhythmbox with a webkit-based plugin. supposedly the store plug in should be able to be used in other music players as well.
all songs are in drm-free MP3 format. when you buy a song, it is downloaded to your Ubuntu One storage by default (this setting can be changed, of course).
I have not actually purchased anything yet, but will eventually. when I get a mp3 player. i don't know which media players will or won't play nice with this thing, so don't ask me.
anyhow, here is a screenshot.
(NOTE: the song playing in my rhythmbox is NOT from the store. I was streaming Last.fm when i took the screenshot)