We created EepURL as a trackable shortening service for MailChimp's built-in twitter integration. At the time, we opened it up to the public, because we felt there weren't enough monkey-based URL shorteners out there.
Alas, we have had to disable the service from public use, in order to protect the reputation of the domain and the high deliverability rates our customers get from our service.
Don't worry. Past URLs are still being redirected, and nothing is changing inside the MailChimp application. EepURL still works fine in the app.
We're basically trying to prevent the URL from getting blacklisted by idiots.
If you're looking to build your own url shortener, take a moment to look at Shaun Inman's Lessn. Building your own url shortener is the best way to avoid having your links connected to a blacklisted domain name.