The Watch List will notify you when two or three tweeps you've targeted jointly follow someone new.  

Good for finding rising stars in an industry, a competitor's new customer, or a new hire in a company.

We DM you personal updates weekly after your target tweeps follow someone new.

To create a watch list, click "create a watch" at the top of the table after you've Twiangulated "common friends."  To edit past Watches, click the "Watch List" link top right on most pages.