How do you decide whether or not to follow someone on Twitter?

Everyone has their own “attention bandwidth” that they can devote to Twitter and other social-networking platforms like Facebook, Identi.ca, Plurk, Pownce, etc. Some people can follow thousands and not bat an eye; others cap their following count at a firm number and have an “add one, remove one” rule.

Here are my own personal heuristics for deciding whether or not to follow someone:

1. Do I feel overwhelmed right now? If not, I’ll probably follow.
2. Have they followed me? Unless they get dinged for some other reason below, I’m likely to follow back.
3. Are they spammers? Dinged without remorse.
4. Do they use a recognizably “real” name, or something like CrazyHippo45? The more real the name, the more likely I am to follow back.
5. Do they use a real photo in their avatar? If not, I’m less likely to follow.
6. Do they tweet consistently? If they have big gaps in their tweetstream I’m not likely to follow.
7. Do they have a reasonable followed/following ratio? I don’t personally care too much about absolute numbers, but if they follow 2,000 people, and only have 20 followers, something smells.
8. Do they post about topics I’m interested in, or topics I’m not interested in?
9. Do they have frequent tweetorrhea (e.g. posting 40 times in any single hour): probably won’t follow.
10. Are they following or followed by people I’m following or followed by? +1.
11. Can they spell? You’d be surprised how important this is to me.

What are your personal rules for deciding whom to follow on Twitter?