If you follow me and it seems like you just follow way more people than are following you (like 500 more people), I won't follow back unless I really like your stuff. If you are following tons of people, you are less likely to pay attention to those you have followed, and I don't think it's fair because I pay a lot of attention to those I follow.
I will follow back if you seem to have about equal followers to follows, even to a ratio of 1:2.
This is my policy so that I don't end up following a bunch of people whose stuff I don't care about :)
