This is difficult...
If I just talk about the different types of teacups, they are rotated pretty frequently. However, I have a lot of "couples" and cups that belong to sets. I, personally, tend to only use one of the cups in a "couple" or one or two of the cups from a set (I don't keep track of a specific cup I'm using when there are many of them).
So, in terms of types, of my dozen or so different kinds of cups, I'd say about half aren't getting much use (all the set cups are included here, and some of my smaller "couples"). In terms of the actual number of cups I have and considering the cups I use everyday, it's much, much less. I'd say I used about four or five different cups every other day... That means over twenty cups are sitting and waiting to be used.
Speaking of unused cups, here's half of a "couple" that doesn't get out much. I found them at a random Korean shop, and they're a little teeny, but I was feeling blue and decided to use one with raspberry oolong.
It was a little chameleon-like in the sunlight.