I currently have over 150 collections, and so every release page I see has over 150 "Add to XXX" links down the RHS of the page.
I use these collections mainly to represent my archived CDs, with one collection per archive box. As such, when I fill an archive, I do not want to add any more entries.

Requesting a readonly (or finalised) flag per collection, such that, when viewing a release page:
a) if the release is in a collection already, the link to "Remove from XXX" should be changed to just state it is in the collection.
b) if the release is not in a collection, only show an "Add to XXX" link when that collection has not been marked readonly.

May well require a schema change.