I've practiced a few times and my record is 184 out of 195. I could get them all if I could see which ones I'd done: I can get them all if I write them all down.
(warning: that website may end up eating the rest of your day, and tomorrow. I'm totally addicted)
edit Or try the Super Iron Man Challenge: name all countries and their capitals. I can barely scrape 50, but I wasn't trying that hard.