Ideal length for a television series?

It seems to me that most television series are seen to have run too long or finished (usually because they've been cancelled) before their time, with very few series being deemed as running just long enough and/or having never jumped the shark by their respective fanbases. So that raises the question, is there an ideal length of time (ie number of seasons or even episodes) that you think a TV show can run without grossly overstaying its welcome or wrapping up far too soon?

I guess the easy answer here is "as long as it's good/entertaining" but if we're going to limit ourselves to real answers, I would have to go for a round number and say ten seasons would be enough time to allow a series to run its course and about as far as a series could go without getting too stale or making too many changes and alienating the audience it found early on. You could go a couple of seasons either way depending on the show but for a quality show that remains well-liked by its fanbase, I think ten seasons is probably as high as you could go without ending too soon or running too long.

Really depends on the show, but I would say the lucky number of seasons is 7. Its a decent length and it ends either right when the show starts to suck or right before that. After season 8 its all rehashes and boat jumping from there.

Yeah, seven's certainly a decent number. Truth be told, I went with ten seasons based on The Simpsons as I feel Seasons 1-8 comprise the "classic" era with nine and ten kind of being on the fringe, passable given how long the series had been running (over 200 episodes through Season 10) and the changes to the writing staff. Even if it had finished its run at 12 seasons the ratio of good episodes to bad would have been more favourable in the eyes of the fanbase.