There is no exact line between a UFO and a WIP for me; indeed, to some extent the only UFO's I will admit to are ripples in the frogged pond.
Though I will admit that sometimes I have ripped out a project because I used up the yarn for that particular project on something else. whoops!
(Speaking of which - what did I do with that crochet afghan I started 8 years ago?)
I'm feeling good today because I picked up and knit on one project that has been sitting in my car as an "emergency knitting project" since August. If I whittle down the number of projects currently on the needle I can treat myself to an orgy of starting new projects.