An Ubisoft representative updated a forum post to say that "it's a problem that occurs when linking your keys to the multiplayer profile. Ubisoft GNS and TG-OPS are currently working on a solution."
Assassin's Creed II PC and Silent Hunter 5 PC both had downtime for legitimate customers after repeated denial of service attacks were made against Ubisoft's authentication servers. Ubisoft maintains that the DRM scheme has not been cracked.
Meanwhile, Eurogamer has learned that the delay hitting the PC version of Splinter Cell: Conviction, which releases 2 weeks after the Xbox 360 version and will use the same DRM scheme, is to polish the game and not due to its DRM.
I suppose the worst thing they could possibly do at this point is announce that their PC titles are experiencing lower than anticipated sales figures.
I don't know if they really are or not, but I will say that I am curious.
That's almost guaranteed to be the case (low sales) as there would have been a nice press release by now saying how great their online DRM is. Even if somehow sales are on par, their tech support costs must have risen substantially over the past few months (if UBI even cares about customers at this point that is).