Well I do know that some modernish sitcom writers (struggling with storylines) have admiited to sitting down with a few boxsets of different sitcoms and, er, borrowing a storyline or two from each one so as not to arouse too much suspicion.
The book I was reading seemed to approve of this method. Hmm, I'm afraid I don't really, BUT, there is little question that most of the fairly obvious sitcom plots have been used already, meaning that even if you or I came up with what we think is an original one, the chances are, it would already have been used somewhere.
Not sure if this is a good enough excuse to simply wade through back catalogues of sitcom storylines and cherry pick your favourites, to me that doesn't seem very creative or genuine, even if they fit your characters. I'm absolutely sure it happens though. When is Miranda on again, btw?