Despite iTunes launching its DRM free store a few months back and recently reducing DRM-free tracks to the price of its DRM-infected tracks, so far it is not clear how well its DRM-free versions are selling compared to its regular DRM protected tracks.  Now, the UK's music store 7 Digital, which has a mixed library of DRM protected and DRM-free music, has revealed that its store's DRM-free tracks outsells DRM protected tracks 4 to 1, which means that DRM-free music accounts for 80% of its sales.

7 Digital has noticed one other interesting difference in the behaviour of customers when it comes to DRM-free tracks in that they are more likely to buy albums than those purchasing DRM protected tracks.  70% of its MP3 sales are part of full album downloads, which means that DRM-free tracks are a benefit for artists and labels interested in selling more full albums. 

At present, EMI is the only major label willing to have its music sold DRM-free by any music, while Universal is still experimenting with DRM-free music with select music stores.  With 80% of 7 Digital's music sales now DRM-free, it is fairly clear that Warner and Sony BMG make up only a small portion of its sales.

Further info can be read in this Ars Technica article.