Really? Though I admit, I haven't seen it used here often. It's Work In Progress. Usually see it on miniature wargaming forums, when people post pics of their unfinished painting projects. Sure, why not on work in progress campaing projects too.
EDIT: Oh, sorry to barge in on this ktkenshinx. Anything with "star wars" in it's title always catches my attention, and since I consider WiP so common abbrevation, I felt the need to elaborate