I'm buying ungodly numbers of books and I'd say more than half of what I get from Amazon is PoD, and print quality varies. In my country (Poland) they have one huge advantage: the price. It's quite often somewhere between 30%-50% cheaper than alternatives which is significant given book prices.

One thing that is pretty annoying is when a PoD book that had colors in the original no longer has them, e.g. on charts, but text still refers to them with color names.

I'll likely stop buying from Amazon too because over the years quality of PoD books also seems to be dropping, it wasn't that bad years ago.