In the last 30 days, according to my Google Reader Trends, I've read over 3,000 blog posts. In all those blogs (about 80) I've come across maybe three or four who use captchas to guard against comment spam. Of the rest, here is the number of instances of comment spam I've come across:
Do they also wear styrofoam helmets about the house, perhaps? People have been known to be struck by falling chandeliers, you know. At least that's what they say.