With all of the data breaches making the news recently (LinkedIn, Tumblr, Myspace), one might wonder if their information was part of what is being sold. This site:
https://haveibeenpwned.com/ checks for exactly that. If you enter your email address, it will tell you if your credentials have been in any of the data dumps that have been reported. It will also email you each time it shows up in any new breach. In the past two weeks, mine have shown up in all 3 of those listed above, as well as two in prior years.
If you are using a password system that would allow someone to reliably guess what your password is on a different site, now is as good a time as any to fix that problem. The best solution is probably a password manager for most folks (that keeps very separate and secure passwords stored, so you only have to mentally capture one reasonably long/complex/safe password to unlock the rest). There are pros/cons to using password managers, but not using them and using similar passwords across the internet for ease of use has no advantages over them (and some obvious disadvantages).
Password manager reviews:
http://www.howtogeek.com/240255/pass...-vs-1password/
http://www.asecurelife.com/dashlane-...rm-vs-keepass/
http://www.pcmag.com/article2/0,2817,2407168,00.asp
and another link to the same "have I been pwned" site:
https://haveibeenpwned.com/