I think that selecting fabrics for a project is the beginning of the project sooooo....I'd say if you are keeping the fabrics together and are not allowing them to be part of your searches as you make other projects they count as UFOs - although I think PIGs is a better description - but if you include them in your selection process when looking for fabric for other projects they are stash. For me it is the segregation from the general fabric population that changes their status!
I keep finding myself pulling out heaps of fabric and setting them aside for projects, then ignoring them, then finding them again after I've just finished a project in which one of the separated fabrics would have been perfect...for years I wondered where all my small blue pieces of fabric had gone, only to find them neatly bundled and lovingly packaged at the back of a drawer waiting to be made into my blue-and-white quilt. (Which I still haven't made.) The blues are back where they belong, in my stash, and are therefore no longer a UFO! *sigh of accomplishment*
Alison