Losing control of any online account is bad news. Hackers have tools which will test credentials using automatic scripts, allowing them to hack tens of thousands of email addresses and passwords in just a few hours. Once this is done they can data mine your accounts for other accounts and information.
You password is not only important to you, it is important to the Internet Community as a whole. Securing your account is one of the first steps in making the internet safer for everyone.
If a password leak of your email address is found, DON'T PANIC, it happens to millions of people. The first thing to do is make a short list of common places that have the same password. Example: is you facebook password the same as your email password?
What's wrong with your pa$$w0rd
How to Use Passwords and Be Safer Online