Gaining followers on Twitter

I have over 200 followers on Twitter. Since last Thursday, in just 4 days, my followers have been doubling daily.

I am also following over 200 people on Twitter. So I am not so successful.
Look at The White House, which is only following 66 but has over 300K of followers (http://twitter.com/whitehouse).

I am taking the traditional steps of 'link exchanges'.
Recently Kevin rose (DIGG) share his insights for how to gain more followers:
10 Ways To Increase Your Twitter Followers (http://www.techcrunch.com/2009/01/25/kevin-rose-10-ways-to-increase-your-twitter-followers/)

He doesn't talk about these kind of link exchanges, but about content and marketing. Learn from the successful Twitterers, and emulate.