A thought:
Seinfeld seems to (on the most part anyway) have been written as a "throw away" sitcom - by that I mean you don't need to have seen any other episodes in order to enjoy one. Am I wrong in thinking that there's no underlying story to any more than 2 episodes (the boyfriend for example)?
I think this is one of the reasons Seinfeld was so popular - you don't have the constraints of having to weave in the main plot line (as in Friends - the ross/rachel thing) therefore not being limited as to what the storyline can be.
In fact, the longer a sitcom goes on, the more these "main" plotlines seem to come into play ie. weak ideas/nothing original left to do.
Anyone agree?