Sometimes your password needs to be changed - either because you want a new one, or you just feel like changing it. So, how often do you change your passwords? Monthly? Weekly?
I change my most important account passwords each fortnight. I'm a little extreme with password, I use 20+ characters with lots of special keys (#/?>^£). All my accounts are stored in my Lastpass, which I change the password and email for every month.
I don't change my passwords, but I do use some very strong and secure passwords for important things such as my email/forum/ftp etc.
I use pretty random passwords but in reality I only change them maybe once or twice a year. Like Soulwatcher I only visit secure and trusted websites.
That's the best approach really. Have a Firewall, anti-virus, and a spyware scanner intact and you should be fine. Random passwords usually don't need to be changed so often - especially if it contains numbers, letters, and symbols.
I change mine about every other month or so, I use secure passwords and never click the "save this pass" popup you get on firefox and/or IE.