Not just a Monty Python reference (hi John!), Unladen Follow is a very neat tool by my pal Allen Pike. It computes, as best it can, how burdensome following a new Twitter account will be. This allows you to avoid the regretful unfollow by deciding before you follow someone whether or not they will clog up your timeline.
Here is me, for example:
I had discussed a tool very much like this on Analog(ue) #17. I knew that Allen had written something like this in the past, but erroneously believed that he had retired it. Unladen Follow is actually quite a bit more than I wanted — it is far more complex, considering many annoying Twitter faux pas in order to assign a Tweet Load score.
You can optionally choose to log into Twitter using Unladen Follow, and it will report to you which of your follows has the highest Tweet Load Units.
Unladen Follow is a great example of why having a robust API can allow for tools that improve your platform, not hinder it.