Here is a great, yet simple sample of a viral campaign. Users got to www.icelandsocks.com select a pair of socks, customize their experience in Iceland by selecting scenes for a video and add subtitles. When you are happy with it send the movie to your friend(s).
Similar aproach as with the Dexter viral, that of I could not have enough and really funny.
It goes with out a saying that this is done to promote Iceland and you flying to Iceland with a local airline, ignore that and look at the video that it generates. It does required a lot of time for the users to do and pass it on.
Go and get your socks!