Between February 28 and May 31, 2005, you can use a special code when you register for your exams and if you fail you'll be able to retake it for FREE. This offer is available worldwide.
I'm going to make use of this offer soon, even if it is to just give me a good piece of mind. I've never failed an exam (knock on wood), and hope I wont need the retake.
More Info: http://www.microsoft.com/learning/mcp/offers/2ndshot/