I own a lot of DVDs - and a significant fraction are still in their cellophane wrappers. I just haven't had the time to watch any of the stuff I've been buying, but there are a number of TV series I'm collecting. I'll watch them eventually.
I have a bad habit of buying shows I haven't actually seen, not knowing whether I'll actually like them, based on recommendations from friends. That's why I own all of Six Feet Under. (And I paid a lot for that... I really should watch it some day.)
Alternatively, some of them I've bought because of the feeling that I should have seen them, usually because it's hard to run a programming department at a convention if you haven't seen what other people are watching. (Primary examples: Babylon 5, Stargate: Atlantis - though I've caught occasional episodes on TV - Superman Returns, Batman Begins, X3: The Last Stand...)
There are even some that I want to get but haven't because I figure I'll never get to watch them, like Alias (at least I saw that one on TV!) and Numb3rs (which I haven't seen - but I have a math degree, so a show in which math features prominently appeals to me). Farscape is another one - I've seen some of it, but not all. The only reason I hadn't bought it anyway is because a) it's very expensive, and b) it's hard to find the full season sets, at least around here. But I hear that the whole series is being released...
Some of these I could probably rent, but the rental places around here make you jump through far too many hoops if you don't have a driver's license.
This thread reminds me... the first half of S1 of FlashForward came out yesterday. Argh.