Each of these are different / unique cases. Perhaps only Facebook actually fits the 37 Signals narrative (that of a company overvalued because people were too optimistic about potential). Zynga and Groupon both had great revenues and from that perspective were deserving of their valuations. However Zynga is losing customers because they didn't innovate in their space and Groupon's financials were misleading in the first place.
Groupon was generating revenues, not profits. They also lied about their revenue declaring their gross billings as their revenue, but they should have declared their net revenue (the amount groupon keeps after paying the merchant) before going IPO ..
