Is there anyone out there that has built an app that grows primarily through (ab)use of social network virality like Honestly? Are you seeing any interesting behavioural changes over time as the population gets tired (or conversely, accepting) of this model?
That we're still putting so much attention into an email like that all these years later suggests that we're never really going to learn or become fatigued. We'll just accept it as "part of life".
http://siteanalytics.compete.com/plaxo.com/
I think they had their greatest moment when Joseph Smarr negotiated the OpenID+OAuth hybrid protocol with Google. Google subsequently poached him. They don't seem to have any other aces up their sleeves to survive.
There's 'make the world a better place' successful, there's 'make something people want' successful, but there's also 'make some cash for yourself and your investors' successful. Sometimes invite spam can get you that last type of successful, which is why we'll keep seeing it.
The worst thing is this kind of crap is very effective. Look at Zynga, they've built a billion dollar company out of it.