I've heard lots and lots of folks talk about the facemask-getting-snagged thing, but in over two decades of boating, I have never heard a firsthand report that it actually happens. Not to say it couldn't, because I have no doubt it can, but personally I think that's not a reason to not get a facemask.
I briefly used one and didn't like it at all. I suppose I could make myself get used to it, but without it, I am quite motivated (a) not to flip, and (b) to tuck for all I'm worth when I do. Since I very rarely flip unless playboating (knock on wood), I find it's not a problem. And while I may think a facemask looks dorky, I won't put it down because I'll look a LOT dorkier if I ever do take a serious hit in the face. I've just evaluated the options and I choose not to wear one.
...and what Mike didn't tell you is that his hockey helmet's facemask is hinged. The flip-up/flip-down factor adds to the "Lord Dark Helmet" effect, since the mask is quite large...
And oh yeah - none of what I said applies if you put a facemask on a Pro-Tec helmet. Then you ARE a dork. I should know, there's one collecting dust in my basement...