Hi!
It seems like the Unread folder in the Sidebar means is:unread in:"Inbox"?
I would be nice if I could save a search/smart folder for unread everywhere (instead of having to search for is:unread manually every time.
Looking through settings, I don’t think “Default Container Folder (folder/subfolder)” is relevant to this? (I don’t understand what it is/does.) 
Also, it would be nice if I could somehow show “All email” for an account, regardless of folder. Makes it easy to see all the latest activity for different accounts.
Maybe some of this should be added as feature requests?
(I think I already voted for Search/Smart Folder in an existing topic.) 