As a series writer, I like to watch how the same characters grow and face new obstacles over an extended period of time, and TV shows are great for that because there is often a new challenge or "bad guy" every season.
I realize as I am writing this that Third Watch has no sweeping bad guy for most of the seasons, and so far in the first season of Smallville the bad guys seem to mostly be a series of incidents with people changed by exposure to the meteor rocks (they haven't yet been labeled kryptonite) and Clark's non-relationship with Lana.
But I expect that Smallville will probably grow into something more Buffy-esque over the next 9 seasons, where rather than isolated incidents there will be isolated incidents and one major bad guy per season (the master in season 1, Glory in season 5, etc.) That happened in Supernatural as well, and if it worked there...
But back to the purpose of this post, watching these shows gives me ideas on how to keep my characters, and my story lines, from becoming stagnant, boring affairs where the same problems keep cropping up, just with different names (any hint that Buffy and the Winchester boys are always facing the same problems will be considered blasphemy).
So to all of you writers out there that write (or plan to write) series, go to Netflix, Hulu+, Vudu, or the video store (if you can find one that is still open) and spend some time watching successful shows that went on for a long time (Smallville and Supernatural had 10 year runs (Supernatural is still going) and Buffy had 7. Not only will it be fun, but you can comfort yourself with the idea that you're not slacking off--you're researching!