When I'm looking at the My Tags page, it says I've used a tag 79 times - but only 77 books are there when I click through to the list.  Any ideas as to why?  What happened to the other 2?

I've noticed this too. I'll bring up a tag I want to close out and remove the tag from all the books it brings up. Then I'll notice that tag on another book sometime later and it'll have more books with the tag.  Why it didn't bring those books up when I brought the list up-I don't know. But it seems to kind of defeat the purpose of tagging.