I have few enough followers on Twitter that every message about a new follower generates some excitement.
Ever since I got my first ever user id on a computer system in 1987, I have always liked my user id at least bear some resemblance to my real name. I have never been much of a fan of l33t-speak nor have I preferred anonymity online.
So, I like to know that there is a real person behind every connection I make on social networking sites.
One test with very low false positive rate for identifying bots or spammers is to check their profile image using TinEye: If you find that the image is used on a bunch of not-so-suitable-for-work type websites or is listed with a bunch of stock photo agencies, you can most assuredly assume that the account was one of many created with the purpose of luring you into following them so they can drive some traffic to various choice web sites.
Of course, not finding the image in TinEye's database does not tell you much.