Just found this article, and a number of others, noting that the 'quartet' ad--shot by DESchatz--was not paid for by Diageo PLC (the 'owner' of Guinness). So this is an interesting problem for Guinness, because the ad gives meaning to the definition of viral; it's well produced, it's reposted by both men and women, and if P&I (that being us) is any indication, many people like the ad. Of course, as a properly civilized company, Guinness has disavowed any association with the ad.
It makes you wonder. The power of influence isn't necessarily governed by intention--we make mistakes, or others make claims on our behalf, and the influence happens beyond our control. Or at least it appears to. This happens in politics all the time and we would be fooling ourselves if we thought that 'accidental' ads weren't a political tool. This one from Obama and this one from McCain, and no doubt a host of other ads that have been banned, are likely to be influential even if those who benefit from them claim no association with them.