When you try to edit a tag but the file is read-only, the tag editor does not give you any kind of notice that it didn't do anything, it just quits. The only way I noticed was that when I corrected some tags, the info kept staying the same in my folder view. I thought Vista was acting up again until I snapped. I don't remember how or why some of my music files are write protected, although I notice that most of the ones I converted from vinyl are read-only, but it is a little bit of a hassle to right click on the properties for each file first to see if the file is write-protected.
It would also be nice to have a way to "mass correct" tags: for example, I usually get rid of the word "the" in artist names, but sometimes I don't notice the "the" that comes in the metadata when I am ripping. A similar issue happens, for example, when I don't notice that whoever submitted the metadata filed artist names as, say, "Cash, Johnny" [which I can understand] instead of the way I prefer, "Johnny Cash." It's faster these days to re-rip than it is to correct, if you notice the error in time.