Zynga made it big on those "free" ringtones that would cost you $10 a month for the rest of your life. Groupon is a ponzi scheme.
Both Zynga and Groupon did quick IPOs because they had to get an exit before they fell apart. Many agents on Wall Street have aided and abetted this (underwriting banks, anyone who bought that stock for you or who encouraged you to buy it, etc.) It's stupid short-sighted thinking from the industry because it harms investor trust (in short supply today) and will hurt future IPOs.
Facebook is a real company that delightes customers. They only did an IPO because they couldn't keep up being a private company the way they were. (Blame regulation) The big weakness of Facebook is an ARPU that's south of $10 a year... It's believable they can get it up, but I' afraid being public means investors will force them to be tactical rather than strategic which could kill the goose that lays the golden eggs.
FB has some real problems, in particular a $10 /year ARPU