Yes, cancelled twice. First time invoked my infamous "Fight the Noteboards" thread.
Why do you say cancellations don't look good? I know for a fact (direct from Adcoms and Admissions Consultants) they ignore cancellations. There's absolutely nothing they can deduce from this. It shows as "taken" on your report, but nothing else. I could have been ill, issues with equipment, got in a car wreak on the way to the center... anything.
As a point of reference: A friend of mine cancelled out during the first 3 attempts, then scored a 740 will be attending UCLA next year.
Please let me know if you've have intel to the contrary...