Most of the comments I get are spam, and most of the spam I get is generic, but in the last few days I've noticed something strange. Before they get down to the business of selling cut-rate pharmaceuticals and porn, spam comments introduce themselves with "Great site! Very informative! Click here for..."
Since spammers are in the marketing business, and everything they do is automated, their market research gets done automatically. So this spam is only common because it works. Someone out there thought "Well. This guy is turning my otherwise decent blog into a Discount Xanax Emporium. But he's so nice about it."