This is a pretty nifty Gmail trick (via TIMELINE via gmailwiki): create a label named "Unread" and Gmail automatically lists all unread email when you call up that label.

Screenshot of Gmail

Seems very much like a half-hearted, half-implemented feature that Google hasn't decided whether to give to users. I for one would very much like to have a standard section for unread mail ("standard" meaning it goes into the same place as Starred, All Mail and co.).