A security breach of RockYou.com revealed that 290,731 users, or almost 1% had chosen the password "123456".
(In fact a large number of users had chosen supposedly "easy-to-crack" passwords. The most common were:-
123456
12345
123456789
Password
iloveyou
princess
rockyou
1234567
12345678
abc123
I cannot believe the 4th one!)