I don't believe I've ever seen a partial match search for tags before; and while I can't claim to know if it's useful for others, whether as a default or even available feature, I would really like to at least have an ability to search for exact match in tags.
For example: if I have both #mod and #commodity tags in my database, I'd like to be able to search for #mod bookmarks without #commodity bookmarks being mixed in.
…Incidentally, some way for case-sensitive search (in tags or otherwise) would be nice as well. The way I discovered this issue was me trying to search for an acronym, but what I got was a bunch of words containing it as a substring (except it was lowercase, even though the search term was typed in uppercase).