'Viral' is little more than a trendy name for 'word of mouth' marketing. This introduction from the Word of Mouth Marketing Association [WOMMA] sets the record straight on a number of issues - follow the links, the content is spread over a number of pages. Interesting is their 'types of ... ' - going by their definitions [naturally, biased to their cause] most of what others might call 'social marketing' is actually WOM. I think they have a point.

Some sound advice on the basics of social marketing [the article also addresses viral marketing].

After email footers, 'email this to a friend' is one of the basic tactics of viral marketing. This article - Optimizing the "E-mail This" Marketing Opportunity - explains how to practice the model [and it's not as simplistic as many assume].

As with social media marketing, I think viral has very limited applications for businesses, with a very few successful campaigns attracting news media coverage that distort the success rate - and ROI. This article - 3 Things Viral Videos Must Do to Make Money - goes some way to setting the record straight.

Realistically, this article - The Secret Strategies Behind Many 'Viral' Videos - could be the only one you need to read on this subject. I love both this article and the furore it causes amongst the folk commenting on it. My view? Did you really believe that the video that launched a new pop career [or whatever] was made by some girly on her mobile phone in her bedroom and then she put it on YouTube and millions of people just happened to see it?
Yeah right - of course it was. Hello, welcome to social media marketing. The conclusion to this article says "You simply can't expect to post great videos on YouTube and have them go viral on their own, even if you think you have the best videos ever. These days, achieving true virality takes serious creativity, some luck, and a lot of hard work." 'Nuff said.

And this one - Making Your Stuff Go Viral - is a watered-down version of the above.