PIN Freq #1 1234 10.713% #2 1111 6.016% Persons date of birth i.e. dd/mm is also incredibly popular. With three guesses you'll get something like 25% hit rate if you know the persons date of birth......
Mine came in an envelope separate to my card that I had to scratch off to see, I memorised that and have used it since. Isn't that what most people do?