Okay, it's not that Matt Smith. But a man named Matt Smith decided the "Doctor Who Experience" in London was the perfect place to propose to his Whovian girlfriend. He even donned a tweed jacket and bow tie for the occasion.
When the other Matt Smith, the one who actually plays The Doctor, heard about this, he sent a letter of congratulations to the couple.
"Matt Smith proposing to his girlfriend! Firstly, being a Smith means phone calls to the bank take so much longer - there are so many Smiths!! But I bet none of them have proposed at the Doctor Who Experience! Amy and Rory would be proud. Next - babies in the TARDIS...? Congratulations to you both and many years of happiness. Love, Matt."