Make it possible to change the library filter by clicking on fields in some way. For example maybe Alt-click since that isn't already used for something else.
Here's a scenario: As I'm looking through my library listing, I come across a book that's part of a series. I wonder what other books are in that series. It's most cumbersome to have to click on the series field in the Info panel, then Ctrl+C to copy it, then type series:" then Ctrl+V to paste then type the closing ". I'd rather simply be able to Alt+click on the series field where it appears in the Library. Similarly for authors (to filter by that author), publishers, subjects, etc.
I like the way you can do it for individual Tags by clicking on the tag over in the info panel. So figure out some way for us to be able to do it with other fields. Thanks.
If enough people comment on this post thinking it sounds like an interesting/useful idea, I'll create a UserVoice suggestion for it.