I have a number of shared passwords, but my biggest problem is that when i register with a site i've used the same (hotmail) email address for years to register with. And what happens when you register with a site? They send your username and password to the email address.
That means that no matter what other site passwords I have, if anyone has had access to my email account, they will know not only what sites to go to, but what the login details are.
Erring on the side of caution I'm cancelling my cards. A frightening number of sites store card details and will let you change delivery addresses.