XKCD is an online comic strip that doesn't do much (or any) marketing that I'm aware of. They inadvertently came up with a great marketing idea out of cynicism. Ask Jeeves is running a "viral" campaign (viral in quotes because it's more stupid than viral) by putting strange phrases on billboards. XKCD decided to target the phrases and has essentially stolen Ask's thunder by grabbing the top spots for most of the phrases after just a couple of days.
If you are thinking viral, maybe you should ensure that you rank for the potential search phrases generated by the campaign.