if the market cap of the company fell below the cash (net of debt obligations) of that company, the investors could liquidate the company, take the cash, and make a profit. thus, it's pretty atypically for market cap to dip below asset value, and even more atypical for market cap to dip below cash holdings.

Actually, finding companies whose market cap is less than asset value is a great way of insuring you're buying shares at a discount. This is pretty rare in technology companies, which are generally valued far above assets, but it's possible to find this sort of thing in more predictable sectors.

For more information, you could look at Benjamin Graham's "The Intelligent Investor". This is a very good introduction to investment, but it's also quite a long read.

Often it means the assets are mispriced (banking stocks....)

Apple came pretty close in 1997 when they had $380 in cash and a market cap of 2.2B but their LT debt was growing fast. ~1B at the time.

Source: http://www.businessweek.com/1997/34/roster34/aapl.htm

So? To "make company private" you have to buy the outstanding shares. 550B+

Yes, at a premium. For example Alibaba announced last month it would buy back its shares at a 46% premium.