I've long thought about the follower/following ratio, though. In a second when a higher "class" twitterer follows you, there's something about their follower/following ratio that indicates the "value" of that follow.
For example, if someone with 20,000 followers and 20,000 following starts following you, it just doesn't seem as "special" as someone with 20,000 followers and 200 following starting to follow you.