I like Big Bang Theory, I have to say. I saw the first season when it was showing on E4, then got back round to it with DVDs of 2 and 3.
I'm not sure how they'll keep it fresh for another three seasons, but then people said the same thing about Friends, and that ran for ten, so I guess anything's possible.
And before anyone jumps straight in to whine abobut how Friends stopped being good, a lot of people, including me, liked the later seasons, at least enough for it to remain as the number one show on television at the time. Just because you didn't like something, or because you can look back now and point out the flaws, doesn't make it bad.