Other hot companies are clearly NOT Ponzi schemes, such as LinkedIn, Facebook and Zynga. Everything is not a Ponzi scheme, but some things are.
Unfortunately most attempts to explain to the general public how U.S. dollars work contain other assertions that are plainly ridiculous (see http://www.youtube.com/watch?v=zXjoAP7jm6Y or http://www.youtube.com/watch?v=_dmPchuXIXQ), and the more tame treatments of related issues lack depth (http://www.youtube.com/watch?v=PTUY16CkS-k).