"During one episode [of How I Met Your Mother], Robin freaks out in a restaurant when she mistakenly thinks Ted is proposing to her after she receives a champagne glass with an engagement ring at the bottom. When Ted tells her "That's not mine," another gentleman at the table behind them says "It's mine," then proceeds to propose to the woman at his table. The proposal between the man and the woman was real. The man set up the whole scheme with the show's producers, and told his girlfriend that they won a contest and got to be extras in a HIMYM episode. Instead, he proposed on camera, and the proposal will live on forever as part of the episode."
Apparently the guy was a friend of one of the writers and after it happened they had to dub in the woman's acceptance due to her being so overcome with emotion when he popped the question!
Is that not awesome or what? High five!