Here's a post I started writing a couple of months ago and left as a draft. I remains true, though Karenann no longer has her own queue so mine has grown to about 45 movies. I think I was going to try to analyze why the queue never really shrinks, but I'll just post the thought as is...
I've been a member of Netflix for several years. I've had my own queue since late 2005. There have been periods where I only have one movie out at a time, and others where I have two.
Originally, I only allocated one movie to myself. Then I watched as the other two sat on the entertainment center unwatched. So I gave myself another slot. I was watching movies far more frequently. I figured that I would process a bunch of movies that I wanted to watch and then give the slot back once I'd whittled my queue down to 10 or 15 movies.
My queue has never dipped below 25 movies.