Re: History lesson
There have always been different classes/categories of shares. It's entirely up to the organisation involved and up to the investor to pay due care. In the UK at least there are various laws around the dissolution(?) of shares as in if you have a particular type of shares these may not be expanded upon and offered to others without being given the opportunity to purchase more at the same effective ratio. Or something similar - in any case the laws are surprisingly fair.
I've often wondered about the exit strategy or just business model of various of these companies. I still don't quite get how FB isn't losing money at a phenomenal rate, on the other hand they have developed, and patented (start argument here) quite a few technologies and they have in their posession a very well profiled database which they can, and are free to, utilise to promote third party services. Even at its most basic level, the hosting, development and support services have to be paid for somehow. If you're ever in doubt, follow the money trail.