The immediate reason for the closure was administration, which is sorta like bankruptcy here in the U.S. The court case against the Motion Picture Association drained the Web site dry, especially after being forced to pay the MPA's court fees. resulting in the friendly “Newzbin Closed” message on the site today.
The site didn't keep any logs to speak of, so if you were a member there's no reason to freak out. I had a subscription once upon a time, and I'm not worried in the least.
There's some sort of mystery regarding what happened to the site's source code. Did someone steal it? Did a monster eat it?
There are, of course, plenty of other Usenet indexing sites out there, but Newzbin was sorta the elder statesman of the crowd. I mean, the .nzb files that people use to download from Usenet do stand for .NewZBin…
Even if all these indexing sites go under, I look forward to reading Usenet the old fashioned way: one group at a time, manually.