I signed up for iTunes Match today, mostly just to upgrade all my music to un-DRM’d 256k (the iTunes Plus method would have cost about $100 at 30c a track). The jury is still out on whether I’ll renew the service next year.
Anyway, it got all the way 100% through Step 1: Gathering information about your iTunes library. and then stayed there for hours. Finally I noticed that a few songs in my library add a little cloud icon with a line through it. Closer inspection showed that those songs were DRM’d and were purchased on my ex-girlfriend’s iTunes account, which I am no longer authorized to use. Deleting, or removing them from the library (if you can foresee a need for DRM’d files you can’t open) will fix the problem.