I'm at 12 or 13 now. Most of them are working! I love my old machines, but I have no where near enough space to have them all out at once so the FW's live in their boxes under the sewing table and the 401 and a couple others are in the closet. I don't name mine but I do love them.
I usually decide which one to use based on what I'm doing. Some machines are better than others for certain tasks. If I'm just looking to sew up something simple, I usually decide by which machine is threaded with the correct color thread.