For those thinking of complaining, some heartening news from the Advertising Standards Association (ASA).
First off, they confirm that viral marketing does fall under their remit: that has only recently become the case adn previously, there might have been no body to which one would have recourse.
They tell me that if an ad has been created by or for an advertiser (i.e. by an agency), and placed by the advertiser with a view to being distributed, this is something they can look at if they receive a complaint about the ads content. This includes ads on youtube.
They add that if the ad has been created by a third party or private individual and placed on youtube, without the knowledge or concent of the advertiser, this should be taken up directly with youtube, who may be able to take action should the content be deemed offensive.
Furthermore, if anyone believes that they have seen what they believe to be an ad subject to ASA jurisdiction, which they believe is either misleading, harmful or offensive, they should put in a complaint to the ASA. They will quickly assess the complaint to establish whether it is something they can address, and if it is not they will point a complainant in the direction of those who might be able to deal with the issues raised.
Best place to start is the ASA Complaints page, as linked here.
There may be some issue as to whether the ad IS an advertisement released by an agency, since there is still argument as to whether Procter & Gamble authorised the creation of the ad or even if they did, whether they authorised its release.
One possible avenue, since the ad is clearly being used to showcase the capabilities of the production company that made it, would be to treat it as, by default, an advert for the skills of the production company.