Not really any info on what exactly happened or what dangers resulted from it. People may want to change their passwords, just in case. I did. I agree with the sentiment here: This is unacceptable from one of the most-visited Web sites in the world. I hope they explain how this happened and what they're doing about it.
itechreport seems to think this wasn't so bad and there is no need to change passwords, though earlier they were suggesting changing any passwords that were the same as your Twitter account.
And there’s no need to panic now or change your passwords. Twitter has confirmed the DNS records were “temporarily compromised” which means user data wasn’t touched and the “hackers” simply redirected users to their own website.
Of course there's no way you can seriously get into the browser market without a pop-up blocker, but wouldn't you also need some degree of ad-blocking to reach the people who would consider switching from the Microsoft-loaded Explorer?