There has been a recent spate of attacks on popular websites like Twitter, LinkedIn, Myspace and now car forums, http://www.zdnet.com/article/hacker-steals-45-million-accounts-from-hundreds-of-verticalscope-car-tech-sports-forums/ where hackers have stolen millions of accounts which include usernames and passwords. This is becoming extremely concerning for people who use the same credentials for various websites, especially sensitive websites like myGov, Internet Banking and work.
Typically, passwords are hashed and salted, meaning that the actual password itself is not saved, but run through special algorithms to generate a different unique set of characters. But given enough information, hackers can reverse engineer and guess the user's actual password, especially if the same one is used multiple websites that have been compromised. Once they have worked out your password, it's a simple matter of trying it on more sensitive websites to steal your personal information, drain your bank accounts and wreak havoc on your life.
The best way to mitigate this is to have a different password for each website you frequent. But let's face it, everyone uses several different websites daily and the sheer number of passwords you'd have to remember would simply make it too cumbersome. Therefore, the next best thing to do is to have a different set of passwords for the more sensitive websites, like Internet Banking, Facebook and work, while using the same password for websites that are deemed "expendable". That way, it won't be the end of the world if a car forum you post to regularly gets hacked. You can simply reset your password and do the same for the other "expendable" websites the next time you login.