My "UFO" are simply those that I don't really want to work on. Normally I will go from Idea to Floppy in about two weeks. I probably completed 12-15 quilts last year, (having my own long arm and a DH that likes to use it helps!).
So when I've got something that has been around for several months, it is one that I've not been all that motivated to get back to.
For me, it's almost depressing to get things organized and out where I can see everything. Sometimes the joy of being able to post a finish is the main motivation to get working on it.
I've not been a very organized person, but I'm making a point to get there (been posting about that on the Mission Organization subforum).