Think about it; even the runaway successes don't make it past a seventh season. With the exception of the original and most recent series, all of the Star Trek series lasted seven seasons. Buffy lasted seven, as well, and BSG lasted four and a bit (The miniseries always feels a little like a season zero to me). The only three shows to break this rule that I can think of are Doctor Who (which ran for 26 years originally, then went on hiatus for 16 years before returning), Stargate SG1 (10 seasons) and Smallville (About to head into its ninth).

The practical answer, I'm sure, would involve actors wanted to stop playing starship captains and go off and do something else for the Hallmark Channel or guestspots on Leverage or whatever; seven years seems the limit on contracts for most actors aside from Tom Welling and Allison Mack. But what keeps SF shows from just swapping out actors and leads like Law & Order and continuing on regardless? Part of me wonders what the fan raction would've been had Star Trek: The Next Generation had introduced the cast of Deep Space Nine into the show around its sixth season and just continued with them as a new Enterprise crew for an eighth, and beyond, with the cast and crew of Voyager joining in at a later date. Could we have had fifteen years of Star Trek, or would fans have jumped ship because their favorite characters were gone?

You could make the argument that no show deserves to run 15 years no matter what the genre; certainly I'd admit to dropping out of er way before the ten year mark, never mind making it all the way to the end. It wasn't that I was bored of the cycling in and out of numerous characters who shared similar traits and ever-increasingly dramatic personal demons, but also that the stories themselves became repetitive and predictable. The same could be said of the final years of Star Trek: The Next Generation, Voyager and Stargate SG1 (and of recent seasons of Smallville and Doctor Who, for that matter). Even the last couple of years of Buffy and Deep Space Nine began to feel stale, as if the writers had told all the stories that they'd wanted to. Is there something about sci-fi drama that exhausts itself in its need to constantly up the scale and scope of its stories each and every year? Perhaps actors seeking greener pastures isn't the only reason why even successful SF ends around the seven year mark; maybe the creators run out of new ideas that they're able to create on a weekly television budget, as well (After all, Star Trek: First Contact was one of the best Next Generation stories despite coming years after the seventh season of the series).

Part of me wonders why we haven't really seen a successful sci-fi procedural set up so as to allow for characters to come and go more freely than a Star Trek, but also to take advantage of a syndication-friendly done-in-one format without the constant demands of an ever-growing internal mythology and backstory... A CSI: Mars, or whatever. The closest things I can think of to that would probably be The X-Files, which tried to replace its stars in its eight season (Hey, another show to add to my list of 7+ seasons! X-Files ran nine, of course) without much success... probably because of the crushing weight of the show's mythos being tied directly to the original leads, and SciFi's Eureka, although that seems to be creeping towards a "bigger picture" backstory ever so slowly. It seems like an obvious idea, considering the success of police and medical procedurals, but science fiction shows always seem to gravitate towards intricate backstories and centering the shows around the characters, instead of the plots, as some kind of cliched way of giving "regular" audiences something to hold onto amongst the technobabble. But, as Lost and Battlestar Galactica push SF TV towards a model of shorter, more novel-like approaches, it'd be nice to see Eureka or even SciFi's new Warehouse 13 demonstrate that SF TV can do something else, and have the longevity of more "mainstream" shows.

90210: It may be one of the buzz new shows of the season, but let's face it: the revamp of Beverly Hills 90210 is never going to replace Gossip Girl (or, if you're me, The OC) in our hearts. After all, who cares about anyone other than the few returning original cast members? We say, use that to your advantage, and reveal that Shannon Doherty, Jennie Garth and Jason Priestly are the only humans left in Beverly Hills, and that the secret story arc of the first season is their slow discovery that every other character in the show is actually a Terminator. It may sound crazy now, but give it a moment to sink in, and then realize that you've laid the groundwork for that Terminator: The Sarah Connor Chronicles crossover where we discover that David Silver was really an undercover Derek Reece all along.

Prison Break: Sure, Lincoln and Michael have already spent three seasons escaping from prisons and getting more and more involved with a labyrinthine conspiracy that threatens to make The X-Files understandable in comparison. But here're seven words that will change everything: Now they're in a prison... in space. Imagine the acting quality of Prison Break mixed with the special effect quality of, say, Moonraker, and the results can be summed up in two words: Ratings bonanza. Who could resist tuning in to see how our heroes could tattoo the schematics of an entire space station on their bodies?

House: We admit it; we're already in love with Hugh Laurie's snarky doctor and his parade of patients with ever more ridiculous and unlikely ailments. We're happy that they're pretty much shunted Cameron and Chase off to the side (If only because we remember Chase's stint on Australian soap opera Neighbours), and we're anxiously waiting to see the emotional fall-out of last season's finale that, yes, may have brought tears to our eyes. But that doesn't mean that sci-fi wouldn't make it better. This is what we're suggesting: Dr. Gregory House, Cyborg Physician. It's perfect! It make his tantrums more dangerous - watch out for that arm-loaded concussion cannon! - and makes his his constant struggle with his own humanity that much more literal. And if you think that Laurie's American accent is good acting, just wait until you've seen his robotic movements.

Law & Order: Criminal Intent: If you've been wondering how Vincent D'Onofrio's Bobby Goren can solve all those cases with just a squint of his eyes and uncanny intuition, we've got the best answer possible - He's an alien. And so is the show's new detective this season, as played by Jeff Goldblum because, well, come on; it's Jeff Goldblum. While the introduction of extra-terrestrials may upset some fans of the long-running cop franchise, we're betting that when everyone else sees the emotional turmoil brought on by the revelation - as well as Goren's sweet new UFO ride - new viewers will be jumping on board quicker than you can say "Alien Nation."

This Old House: Admit it; you've been a fan of PBS' long-running home improvement show since Steve Thomas was a host, and you're wondering what science fiction could do to give Norm Abrams a new coat of paint. Well, we're suggesting that producers keep the name and start over from scratch. I mean, it's one thing to spend weeks watching people put up drywall and talk about plumbing, but what if the title of the show was taken literally, and Norm, Kevin O'Connor, Tom Silva and the rest of the crew travelled back in time to view the original construction of the houses in question? Just imagine the excitement of watching fine Bostonians dealing with squalid conditions in the late 1800s while trying to see what kind of lumber was used, and then get upset that PBS' budget doesn't stretch to the research, experimentation and materials necessary to create a time machine.