Twubble supposedly uses your friend graph to gather and give you a list of others you may like to follow. You click the button to start the collection of your friends. It then finds those you follow and starts scanning their friends. I can see this taking some time if you have a large pool you follow and then that next person has the same.
It started creating a list of people to follow that more than one person that I follow, follows. Whew! Basically if I follow four people and tow of them follow one person I don’t, then it suggests them.
I liked some of the suggestions and they made a lot of sense. I actually added some new people to follow.