My site, The Hop Press, http://www.hoppress.com/ stopped working when the links no longer functioned.
I have no idea what might be wrong.
To my knowledge no one has changed any of the code and authors are not able to upload their own widgets/plug ins.
A remote chance is that permissions changed on files but I'm not sure what problems might be caused by that that would result in all the links failing.
I do get a prompt to upgrade to WordPress MS from WordPress MU (that fails however due to a bad URL).