I've personally yanked a laptop off of a dining room table by tripping over the cord, but that was many years ago. But more recently, my 4 year old has pulled the mag-safe adapter out of my MBP a couple of times. Someone I used to work with had the unfortunate experience of having part of the AC adapter plug break off and get stuck in the side of an older MacBook. That was an impossible fix.

So, here's another data point or two... I've been very happy with the mag-safe adapter. It's one of those things that you don't need until you do. And if you don't have it, you could do some real damage.