There is a simple formula to determine how successful the stars of hit television shows go on to become: how long it takes before the reunion special. Seinfeld held out for 11 years, how long did everyone else last?

The assumption when any television show hit ends its run is that the stars will go on to fame and fortune and other projects. Sometimes that happens and we never hear from them again (see Friends and inexplicably Full House) but when it doesn't, they all rush back to familiar territory to jump start their careers. Here's are scale from the worst to best.

Dynasty
 Final Episode: May 1989
Breakout Stars: Heather Locklear, Emma Samms (just kidding)
Reunion: Dynasty: The Reunion aired in August 1991. The came back for another go-round Dynasty Reunion: Catfights and Caviar in 2006.
Cause: There were some cliffhanger plotlines to tie up, and really, nobody was doing anything else. Also, shoulder pads were about to go out of style, so they had to do it to save on the wardrobe budget.
Held Out: 2 years
Respectability: So bad it's campy.

Firefly
 Final Episode: August 2003
Breakout Stars: Does anyone beside us and hardcore Joss Whedon fans even remember this?
Reunion: Serenity hit movie theaters in September, 2005
Cause: To try to get someone, anyone, to finally watch this thing. It failed.
Held Out: 2 years
Respectability: Did it have any to start with?

Sex and the City
 Final Episode: February 2004
Breakout Stars: Sarah Jessica Parker, who was the biggest show when the series started. Everyone else found out there really aren't any roles for women over 30.
Reunion: Sex and the City: The Movie came out in May 2008 and broke box office records. A sequel is planned
Cause: These ladies needed a way to make some money. And, obviously, cosmo-swilling Midwestern "fashionistas" demanded it.
Held Out: 4 years.
Respectability: Shameless.

The X-Files
 Final Episode: May 2002
Breakout Stars: David Duchovny, who was only a recurring character on the show's final two seasons, is doing quite well on Californication.
Reunion: X-Files: I Want to Believe, the second movie based on the show, failed at the box office in July of 2008.
Cause: We still haven't figured this one out.
Held Out: 6 years.
Respectability: Pretty lame.

Seinfeld
 Final Episode: May 1998
Breakout Stars: All of them, but the biggest has been Larry David, now of Curb Your Enthusiasm who wasn't even an actor on the show. Julia Louis-Dreyfuss is still holding down The Adventures of Old Christine. Jerry Seinfeld sits in his house and counts his money, only leaving occasionally to do stand-up, American Express commercials, and The Bee Movie. Jason Alexander had a few failed sitcoms and KFC commercials. Michael Richards had a racist rant that ruined his career.
Reunion: On the cover of Entertainment Weekly August 2009.
Cause: They'll all guest on Curb Your Enthusiasm this year, where a Seinfeld reunion becomes a meta plot point. For a giggle. They're all still rolling in residuals.
Held Out: 11 years.
Respectability: High.

Facts of Life
 Final Episode: May 1988
Breakout Stars: Nancy McKeon was a Lifetime fixture before going to rock the tween set on the Disney Channel's Sonny with a Chance. George Clooney did two seasons.
Reunion: The Facts of Life Reunion aired on ABC in November 2001
Cause: Because the gays thought it would be fun and Mrs. Garrett wasn't getting any younger.
Held Out: 13 years.
Respectability: Surprising good. This also seems to be the exception that proves the rule, either that or all the girls have given up on acting careers.

Saved by the Bell
 Final Episode: May 1993 (we're not counting The College Years, which ended in 1994)
Breakout Stars: Mark-Paul Gosselaar did the later seasons of NYPD Blue and is now a hit on cable's Raising the Bar. Tiffani Amber Thiessen did 90210, Two Guys, A Girl, and A Pizza Place, Fastlane, and Good Morning, Miami. Elizabeth Berkley did Showgirls and became a Hollywood punchline, Mario Lopez danced with stars, and Dustin Diamond released a sex tape.
Reunion: The cover of People in August 2009.
Cause: Because it was either that or Jimmy Kimmel.
Held Out:16 years.
Respectability: Amazing!