I've just taken a look at the memberlist, and almost half of the usernames on there have no posts. o.O
I guess many of them have at least one picture in their gallery, so the total count of "non-interacting" members (and inactive for at least a year) is probably significantly lower. But still, it may be in the three-digit range!
The ones I was thinking of were those who have logged on since registering, but have done nothing whatsoever on the site - no posts, no gallery comments, no pictures, up to around two years ago. Anyone who has registered or interacted in any way within the last couple of years or so, they're fine.
Nothing has been decided on that as yet, anyway.