hitman--
I'd love to see hyperlinks incorporated in MC, for a variety of applications which are probably best left for MC 13.
Regarding "covers", I've been stuffing this annotation into my custom "version" field, which has now become semi-colon delimted and more or less useless for browsing.
As far as annotating track name, I think that's a bad idea for several reasons. The biggest for me: MC's search engine has no "fuzziness" to it, so say if you are listening to Neil Young's "Down By The River" and want to right-click/locate/name to find all covers of that song (there are about a half-dozen, most of them in my library), your search won't bring up "Down By The River--Cover", etc. So as best as I can, I try to homogenize the naming and put annotations like "extended" "live" "cover", etc into other fields.
On the other hand, I do try to inject annotations into my file names. This is to try and avoid overwriting or "deleting duplicates" when in fact they are not duplicates.