There are quite good methods, which i have mentioned here at - http://www.thewwwblog.com/how-to-make-money-with-twitter.html
Its depend on the quality of the follower. In my case,i only have around 100++ follower,but their buying power is high,it manage to contribute around 5% to my product sales.
I wouldn't look at how many followers to aim for, but how much awesome content to aim for. I know people making cash off less than 100 followers... And then others who aren't monetizing 3K+. All depends on what you're saying!
You create a "Master of Your Niche" twitter, or a "Internet Marketing Guru Twitter" and get people who are interested in the same thing to follow you. Hint, follow the followers of people who in same niche. Then sell them stuff.
Sizzler methods are nice; any more ? Because people talk here about monetizing this and that, but *how*
There are really only a few ways to monetize Twitter right now. At least that I can think of. 1. CPC text links. Tweet them, people click. I prefer this method. 2. Sell your tweets. You can't do this on DP, but outside you can. Don't do it too much though. 3. Use Magpie. Yes, it tends to be annoying sometimes, but if you are very active on Twitter, and post lots of original stuff, then one ad every now and then won't hurt you. 4. Sell your background. Using something like Twittad. This won't get you as much as selling posts, but it is an option. I use a combination of all four of these. It seems to be working quite well.
Another idea is to make active sales by searching for potential customers interested in your products/services and providing value for them by answering questions and useful information for their niche. It may seem more complex, but selling stuff directly from yourself is, in general, more profitable.