I was just recently looking for a simple password manager for Ubuntu, and Seahorse is so close. It unlocks with your login key so if you're logged in you don't have to keep entering a master password each time you need to retrieve a password; it stores everything in one easily-copyable encrypted file; and it's a core part of GNOME. But you can't store any metadata about the password, like a username! And that makes it completely useless as a serious password storage interface. What good is a password if you can't easily store the username along with it?

If only someone would update Seahorse to store optional metadata along with passwords...