About a year ago I wrote a script that crawled my Twitter network and made me follow lots of new people. Then it waited 24 hours to see if they followed me. If they did, I kept them in my list; otherwise, I chopped them. After a couple of days I had almost 600 followers. I just did this for fun, and I knocked it off after a couple of days for fear of being banned.
I wish I'd recorded stats from the beginning of the experiment, but I only started recording them in August (2009). This is what it looks like so far.