No, plenty of activity on the mailing list, and a new release was in December. Also maybe try nunit.com instead.
There website still works for me. I wouldn't worry about the latest releases as it's pretty much complete for the simple task it does.
I predominantly still NUnit that's largely because it's supported by R# in VS.NET also there is a great ecosystem surrounding it allowing you to seamlessly integrate it into most automated test suites and Continuous Integration solutions
As far as I know there are often DNS problems with nunit.org. nunit.com usually works and is up to date.
The NUnit team no longer uses Sourceforge. The project is now hosted at Launchpad (https://launchpad.net/nunit-xtp).
The DNS problems have been intermittent over the past year, with increasing frequency. I'm working on a temporary fix - using a different DN server - and will be moving the site to a more reliable host. (Current host is seekdotnet, btw)
I've also made the notice about our moving on Sourceforge more prominent. We've been on Launchpad for quite a while now.