NNDB, a directory of important people and celebrities (the two are not exclusive) standing for Notable Names Database, has put together a mapping tool that lets you connect the dots to see how people are intertwined.
One example, featured in this demo video, shows the overlap of board members for large tech companies, including Apple, Intel, Yahoo, and Microsoft. You can use the tool to figure out who's worked where, then drill down to their personal histories--both work and play, with very little effort.
The backgrounds of each individual are maintained by the NNDB community and its editors. You can also go in to create your own charts, though you're limited to NNDB's directory of people and companies.
I was going to do one for, but alas we're not there. You can, however, compare CBS to NBC, ABC, and even Fox Broadcasting. There's not a lot of overlap, but you can easily see people's positions at the company and where else they've worked.
This reminds me a lot of Cogmap, a service that lets you map out the hierarchy of your workplace. It's got a little more flash, though, and is similar to They Rule, a site outdated about four years that chronicles the "ruling class" of corporations around the world.
For those who are less corporate-inclined, some of the celebrity "maps" are pretty amusing, including charts of who's been romantically involved with whom.