As those companies have huge exits, there's going to be a lot of young, early employees that are able to cash out and become angels or work on their next huge startup.
Some people say it's a bubble. I'm thinking/hoping it's more on the lines of a Renaissance.
This process actually started happening a few (2) years ago, and has been picking up the pace increasingly in the last six months. Much of the recent rounds of financing has been going to early stage employees who are selling off as much as 30% of their holdings in these "Pre-IPO" rounds.
If the IPO windows doesn't open up again, fairly soon, many of these employees will be fully vested and onto their next thing before their company goes public.
At least some of those companies have actually turned a profit and stand a chance of maintaining one. I have my doubts about Groupon's and Zynga's medium-to-long-term chances, but I've been wrong before.
there's going to be a lot of young, early employees that are able to cash out
Early employees will probably not be able to cash out for at least six months; that's the standard waiting period after an IPO. Ironically, people who get friends-and-family deals pre-IPO are the most likely to get rich quickly (if they sell on an early uptick).
Tamagotchis were highly addictive and demanding of attention in their heyday.
They've taken one aspect of WoW, the one everyone talks about and the single most addictive quality -- I agree. But people stay with WoW for more reasons than that. People who get addicted to leveling up get over that addiction sooner or later, and usually sooner.
Zynga is a one-trick pony, so far. That's why I have doubts about its long-term viability. Unless it comes up with something based on another paradigm or makes the games more interesting, they will lose the momentum they've got and crumble. You can't fool all the people all the time.