Spoilers - a statute of limitations?

This morning, on the drive in, my carpool mates and I were discussing spoilers, spurred by yesterday's strip over at Penny Arcade. At first we chuckled at the strip and agreed, there has to be some manner of statute of limitations - at some point, these things become a part of the Collective Consciousness, don't they? Certainly, a mainstream movie, released in 1933 fits within the realm of "OK to talk about openly."

But then, if you've ever had something spoiled for you, something that you actually cared about or paid good money for, you know how frustrating it can be. I've had a suspense movie ruined for me by the person behind the snack counter after I'd bought my movie tickets. I was, needless to say, a bit peeved. Clearly, a movie still in the theaters should have some sort of protection, but conversations within our own office here have proven that to be untrue.

So, where is the line? Is it a time limitation? Is it a certain amount of box office take, suggesting a critical mass has seen the film? What about games, which are, to date, a less mainstream media? Should games have a longer statute of limitations, so that we don't spoil all the best parts of the Great Games of the past for newcomers? Should niche media self-regulate spoilers to encourage growth? Can we get past our desire to seem the All-knowing, All-seeing, been-there-done-that veterans of the Gaming World?