One thing not touched on regarding the strategy of following a lot of people. Whenever you follow somebody new, an email is sent to that person. For people who already have lots of followers, this may get lost, but for people who use Twitter relatively casually, getting this email along with a sample tweet is a great way to get introduced to a Twitterer that they may be interested in.

It may not be the intent, but it works well as an announcement mechanism as long as you remember that not everybody uses Twitter for business reasons.