Maybe I should explain a little more ;)

I use the project manager to frequently switch between files in the project, and I have a lot of files so it's quite full. Often I find I want to go back to the previous file I was in. I have to move my mouse to the project manager then scroll up/down looking for the previous file (often I've even forgotten its name - because I'm focussing on function/subroutine names not filenames).

It would be nice just to be able to hit "back" and go back to whatever file you were in.