Looks like 2008 might well be the year the DRM wall comes down.
Amazon announced today they plan to (licensing allowing) to extend DRM music sales beyond the US.
As the DRM free purchase model market expands via different suppliers, I suspect a segment of people who have legitimately purchased music in the past from say, iTunes, will now become aware of the DRM locked-in library they have invested in. They might not want to pay again, or perhaps they wont care....
iTunes Plus for a few months has opened a route to allow users to "upgrade" to some previously purchased music to DRM free, but I've not seen any news on the uptake of that service.