My allies at "TVaholic" (although they're probably not even aware of my existence, even though we're both members of "Friends of Bill Paley"......) have supplied this telling dialogue exchange that forges a new link in the TV Universe:
Show: The O.C. (FOX)
Episode: The Cold Turkey (Season 4)
The Setup: Summer and her father are talking at the airport as she is heading back to college. Her dad may be accepting a job at a hospital in Seattle.
Dr. Roberts: It’s so crazy. To think the next time you come home I may not be living here.
Summer: Yah, are you going to take that job in Seattle?
Dr. Roberts: Well the offer came at the perfect time. The hospital is famous for being wonderfully quirky; it’s called Seattle Grace.
I'm trusting in TVaholic's transcription as being correct, as I don't watch the show. (I've only seen two episodes: the one with George Lucas, and the one in which Mischa Barton kicked the bucket.)
It reads rather clunkish, and I guess it would depend on the skills of the actors involved to make it work. But even if these lines were delivered by Mrs. Higgins' third-grade class, they remain true to the Toobworld tenet that if it's broadcast, it's part of the TV Universe. So this would be a legitimate link between 'The O.C.' and 'Grey's Anatomy'.
Now if only we could get some other show that's part of the "official" TV Universe, it would be a cause for joy among the Westphallians....