I don't count unquilted tops as UFOs, they are a finished project -- just not a finished quilt. I have way too many unquilted quilts
but I have very few UFOs (mostly because I got rid of most of them either by doing or finishing). I do have a couple "works in progress". Some times that work is rather far apart.
I mostly work with scrap/charm projects, typically using no more than 1-4 pieces of any given fabric and it can take me years to collect the fabric, at a certain point I will make a "project" box even if the only project is collecting the fabric.
I write myself notes on where I am in the project, typically with an EQ pattern enclosed. It might not say much, like I finished making Postcard blocks, just a simple postcard sized piece of fabric with a narrow attic window setting. Then I'll put it together with black sashing (fabric just came Saturday, is washed and ironed and ready for cutting). The note isn't much, it just is a printout of the top with simple hand-written notes like: Need 68 blocks. Attic Window & Sashing finishes 1.5, cut 2", but that's enough to keep me going.
The way some of you consider UFOs then every magazine or fat quarter collection someone gave me might as well be an UFO!