Coincidentally, Metafilter points out an impressive compendium showing how a good chunk of what's on TV can be tied back to the musings of a single autistic child in St. Elsewhere.
In the final moments of St. Elsewhere, it was revealed that a character, autistic little Tommy Westphall, imagined the entire series' run. Because characters from St. Elsewhere crossed over with so many other shows (many produced by Tom Fontana), and because these shows had other crossovers, industrious web-inclined TV-watchers have catalogued the links... 164 series are involved, from Law & Order to Friends and Seinfeld, propagating backwards to I Love Lucy and Andy Griffith.
Some gems from this text list of crossovers (liberally trimmed here):
Diff’rent Strokes’ Arnold and Mr. Drummond considered buying the home of The Fresh Prince of Bel Air’s Banks family.
The Jefferson’s George and Weezie were also potential buyer of the Fresh Prince home.
E/R’s Nurse Julie Williams was related to The Jeffersons. And George Jefferson appeared on E/R
The first All in the Family spinoff character was Maude. Maude was Edith Bunker’s cousin.
Maude’s Florida Evans spunoff onto Good Times.
The Nanny's Fran Fine and Everybody Loves Raymond's Raymond Barone went to high school together.
Ellen meets Stanley Roper of Three’s Company while looking for a roommate.
Mad About You's Paul leased his old apartment to Seinfeld's Kramer.
Some of these links I knew, many I didn't. The connections are pretty random, but that fits into idea that all television is a child's stream-of-consciousness.
And from another site, which posits that every TV show falls into one of just 36 fictional universes, it's revealed that Knight Rider and Star Trek are linked, through the mad-scientist creator of NOMAD. They're apparently not counting James Doohan's appearance on KR2000.
I think the collectors of these crossovers may tend a little towards autism themselves. But I find it actually comforting to imagine much of our entertainment is connected. And now that William Shatner sings (speaks?) with my favorite musicians on "Has Been" (in what critics are calling in among the best albums of the year) we're moving toward consilience.