About 8 songs per year, all of which went massive (at least in the US).
And I was expecting that at some point I'd stop recognising them, as I didn't think I'd been paying any attention to pop music recently.
Watching this reminded me that I've pretty-much _never_ paid attention to pop music, and indeed my osmosis seems pretty constant all the way through - I recognised about 25% of the songs from each year.
(I have no idea how, for most of them, as I don't tend to watch music videos. And I don't think I've ever watched or listened to a chart show in my life. I assume that some things are just unavoidable if you ever leave the house.)
Original post on Dreamwidth - there are comments there.