Here's what I'm thinking.
If I open a playlist by clicking the tab-bar and choosing "Load playlist..." it opens up all nice and fine. If I then add files to this playlist and want to save it I have to relocate the dir. type in a name (ok, I could click the original file but I want you to know how much work it realy is:) and then save it. Phew, that's a lot of work.
So, why not add a "Save Updated Playlist" to the menu? As you probably've figured out by now this would save the playlist with the same name and in the same dir. as I opened it from. Is it just me who finds this useful?