I need to apologize to my commentators. I only realized that I had a spam comment tab recently, and I found a bunch of great comments buried there - some from 2011!
About half of the comments flagged as "spam" were legitimate, which is only slightly higher than the proportion of spammy comments that aren't flagged. I didn't see any trend, except that comments mentioning salary were flagged at a higher rate.
So now I know to keep track of spam. I appreciate all the new features that have been added to blogger - I guess I should poke around the available features more often.