[kevinpet]

You can buy before the IPO, but you won't have anywhere to sell them. Buying before IPO is risky because you may face taxes on the difference between the strike price and fair market value, but not be able to turn any of the paper profit into actual cash to pay the taxes.

[arfrank]

Wouldn't a website like secondmarket.com allow you to unload stock before a liquidity event? That assumes that someone would want to buy the stock from you.

[seanc]

No, it's a private company, and part of the ownership contract will prevent you from selling your shares to people outside the company. You might even be precluded from selling them period. That's why most people don't buy until the company's exit.

See my mainline comment for more details