The TV theme song thread got me thinking about the phenomenon of shared TV worlds

For instance;

1. Beverly Hillbillies were in the same TV world as two other sitcoms---what were they?
2. Rockford files shared TV worlds with which other private eye?
3. What two other sitcoms were in Laverne and Shirley's world?
4. Anyone remember which character from M*A*S*H had a short-run series?
5. Law and Order just shared cops from another series. Which one was it?
6. What is the longest-continuously-running "world" on television?
7. The new Dick Van Dyke show "Diagnosis Murder" (and a sorry-ass, lame, career capping series it is) combined the "worlds" of what private dicks?
8. Much to Archie Bunker's chagrin, whose world did he share?

Anybody know of other shared TV worlds?