Looks like Twitter is making an effort to fight malicious URLs and attacks taking advantage of twitter to spread. Any effort is good in this day and age. A few things I'd do differently would be to disable the URL in the email that is sent to the user informing them that their tweet is being removed. The drive-by url was live and clickable in the email I received.

Also, I'm assuming that Twitter is using something like the Google Malware API to check for malicious urls in the posts. The assumption would be that they are following the links in the shortened URLs like bit.ly, etc...

How about sites that redirect to a drive-by url or a compromised legitimate site with iframes embedded?

Regardless it's good to see that they're taking an active role in trying to mitigate Twitter as a delivery mechanism.

/dean