Lauren Cooney at IBM came up with this idea on her blog:

What I'd like to see? An app that utilizes the Open APIs that Facebook and Twitter have so that I can figure out which of my 500 FB friends use Twitter. Anyone interested in building this for Web 2.0 Expo? If so, I'll buy you a beer next week. If you use Social Graph to build it too, that would be pretty neat... is it possible? /LC

Since I'll be at the Web 2.0 expo next week at the Silverlight Booth (April 24 & 25), I thought that this would be the perfect opportunity to introduce her to Popfly our tool for creating Web 2.0 Mashups! 

I created this mashup in about a 20 minutes (I had to create a block that did the matching of names - that's why it took so long).