If this is the same AF Holdings/Prenda Law that we've been reading about on Popehat for a year, it might be tough to extrapolate this ruling into any kind of "crushing blow" against the concept of trolling; it would be understating it significantly to say that Prenda was already "on the ropes".

http://www.popehat.com/tag/prenda-law/

(Popehat's coverage of Prenda is golden; a highly recommended and amusing read.)

Later

Having read the opinion, it's a little of both. (I'm not a lawyer and expect to be corrected here).

First, the Appeals court ruled that Prenda/AF's attempt to compel service providers to cough up records created an undue burden on the providers. That burden was undue because in attempting to do that, Prenda/AF needed to demonstrate a good-faith belief that the records they were speaking were discoverable.

The DC circuit points out that it would have been possible to file such a suit and make such a demonstration, but, of course, Prenda/AF did not do that.

Second, the court ruled that Prenda/AF's attempt at joining all their 1000+ suits into a single case was invalid, because Prenda/AF didn't demonstrate in a meaningful way that the cases were related. Again, the court explained that there was a reasonable way Prenda/AF could have legitimately filed such a case (albeit with fewer defendants), but the slapdash way they actually filed the case made it easy to reject their joinder request.

To the extent that the details of this ruling pertain to the specifics of the Prenda/AF case, they are less useful, because you'd have to imagine after reading more about Prenda/AF that any copyright troll in the world would have to be smarter than them.