They say there's "no evidence that customer passwords were taken", but they''re pushing out password changes to everyone just to be safe. In addition, you should change any of your other passwords just to be safe -- that is, if they're at all similar to your DreamHost password. Just as we did during the Zappos hack, we highly recommend you set up a password manager like LastPass, and use it to help you audit your passwords. Remember, the only secure password is the one you can't remember. Hit the link to read more.
Changing Shell/FTP Passwords due to Security Issue [DreamHost Blog via Hacker News]