Rules and conventions about when to use and not to use commas are legion. But certain errors keep popping up. Here are a few of them.
I wouldn’t normally link to something like this because 1. it’s about American English so the rules don’t apply 100%, and 2. I find American grammarians tend to be overly fussy. I was just tickled by how the correction to the article was a perfect illustration of Muphry’s [sic] Law.