A feature I think would be a nice addition would be "Close Other Files", which would do a Close All except the one you are working on.
Most of the time when I open PB, I am going to be carrying on working with my previous files (current behaviour is good!), however there are times when I double click on a .pb file to open it from explorer, just to have it open another half dozen tabs of other files, and then I find myself going to Close All, and then open the original file I clicked on in the first place.