I like to not count quilt tops waiting to be quilted, I've got about 25 of them at last count.
I typically only work on one top at a time, and get it to "ready to quilt" stage before starting another. But then I have 3-4 really long term projects (near UFO's) that I pull out when I'm done with one top and not quite sure what I want to start for the next one. They are ones that are very time consuming, and after several days I'm ready to move on.