If you have an Adobe account, even if you have not received an email from them, it would be best to log in and change your password.
For those of you who ignored the emails because you thought they were spam... you didn't do anything wrong. I always urge customers to be suspicious of emails like that, even when they turn out to be legitimate. In the event you receive a similar notice in the future (from Adobe, a bank, Amazon, etc.), I advise customers to ignore the links in the email, go to the site in question, and look for information about whatever was presented in the email. Even if you just go to the potentially affected account and change your password without confirming the threat, you've done nothing but protect yourself. Just be wary of links in emails. If you're going to use them, make sure they are taking you to the proper places.