Okay, not viral, but I think there has to be some psychological hook for the worker that gives them benefit for the small barter of time and effort. Novelty gets you in the door, maybe boredom, but then again if I am bored, I can always just start answering election year push polls.

Some way for workers to see value besides karma or a pay rate of $3/hour is what I haven't figured out yet.

Viral in the classic sense might not have described delicious, but I will say that I had a much richer and more interesting and more professionally useful social network of followers and followed people on delicious than any network since...Twitter is the heir for this kind of network-filtered firehouse of interesting stuff, and Quora almost could get there, but delicious had more impact per byte than either of those. I always considered it somewhat viral in the sense that I had maybe a dozen coworker colleagues I followed plus a smattering of random people who turned out to essentially be high-signal, curating SMEs for various interest areas I needed.

I am working on prototyping ideas as time allows, but still working though the examples so far.