I love the fast search capability of GMail, so I’m forwarding all my mail to it. But that also means there are times when I have quite a lot of “Unread” mail. Gmail is only showing mailboxes in pages, so there’s no easy way to quickly have a look at all unread mail to “mark as read”. At least not in the UI. But you can get a list of all unread mail by simply searching for

is:unread

This is just an Advanced Search. Want to play with those a bit more? Check the Google Advanced Search-help page.