If you haven't seen it, do so immediately. It's funny, it's silly, it's charming. Peter Davison leads Colin Baker and Sylvester McCoy on an epic(ish) quest to appear in "The Day of the Doctor". It's a half-hour of Whovian goodness.
edit: There are a ton of cameos, inside jokes, and self-effacing humor. I don't want to spoil it - the fun is in the surprise - and it definitely works best if you've already seen "The Day of the Doctor".