It seems to me, I might say, that season 7 is not a good season for a TV show. Maybe it's self-evident - that much time and a show can run out of steam, the original creators got bored and left or were forced out, but if a show even got that far, it must've had something going for it. One might argue, successfully, that season 7 was among the best ever produced on The Simpsons, but most shows, judged exclusively on #7? Not renewed for the coming year. Some shows even improve in quality after getting the miserable seventh out of the way...
The list so far - confirmed as having poor seventh seasons: Homicide: Life on the Street, The X-Files, Mystery Science Theater 3000, CSI, The Sopranos (6 part 2, 7, whathaveyou), Smallville, Buffy the Vampire Slayer, Cops, Law and Order: SVU, Saturday Night Live and Friends.
Rumored to have had successful seventh seasons: Stargate: SG-1, South Park, Simpsons, Seinfeld.... we've almost got an S-exception to the rule.
As of yet neither confirmed nor denied (mostly sitcoms or WB fare): M*A*S*H, Cheers, Mad About You, Full House, Charmed, Dr. Who, Gilmore Girls (remember, we're saying relative to each show's other seasons, not against all shows ever), The Cosby Show, Gunsmoke, Home Improvement, Walker (Texas Ranger) or Dr. Quinn (Medicine Woman), ER, 90210, Macgyver, Dallas, LA Law, Bonanza, Knots Landing, Are you afraid of the Dark?, Tales from the Crypt, various Star Trek shows, and probably a bunch of reality shows - Survivor, Real World, Road Rules, American Idol...
Shows on the rain-slick precipice of DOOM: 24, Curb your Enthusiasm, Mythbusters, The Shield, and Ice-T's Rap School.
Anyone got any to add or to confirm or deny?