Tab-less mode.

I work with projects that have a lot of files -- far too many to have a tab for each one. Instead, I just look at the project drawer for modified files, and hit Command-Option-S to save them all. The tab bar serves no purpose, and is quickly cluttered up with hundreds of open files. I might as well be able to hide it. Even better, it could automatically close any un-modified files as soon as I browse away from them.

Alternatively, some sort of intelligent tab mode that would promote the most recently used tabs to the left side could be helpful.

For a good example of how it could behave, check out Notational Velocity, which doesn't even require you to tell it when to save.