If anyone wants to learn a little something about online viral apps, walk through Flixter.
First, I got a message from someone who accidently uploaded their whole address book and sent invites to take a movie quiz. Loving movies, I signed up and took the quiz, but the whole while, it made a big point of getting me to invite my friends, and then it had me paste a MySpace bulletin as well as a widget in my MySpace movies section... automatically.
Plus, smartly, it tells me when friends of mine have answered my quiz and coaxes me to go online and see how we match up.
Admittedly, I haven't gotten into much of the depth of the product.... I'm not sure they've developed enough hooks yet to pull users deeper into the system to encourage more movie ratings, but that will come in time as they grow their community. For now, I can see how this is going to grow like a weed.
Of course, I'm ceonyc on there, too...