Twitch just announced that “there may have been unauthorized access to some Twitch user account information”. As a result, they have expired all passwords and disconnected accounts from Twitter and YouTube, which sounds quite serious.
This one sounds kind of bad, though it could be that Twitch are just being cautious. They advise users: “We also recommend that you change your password at any website where you use the same or a similar password.” That suggests that a lot of passwords and user account info leaked.
So if you have a Twitch account with a common password, it sounds like you should probably start battening down the hatches and making sure your other accounts are secure.