Let's see, a stock price of under $20/share previous to the $31/share offer being made. A greater than 50% premium is massively undervaluing the company?
Granted the market is not a perfect indicator of true value of a company. Google was a good example of this when they were valued at around $100/share and then proceeded to quadruple in value over the next 2 years.
However, Yahoo is no Google. They have not been able to effectively compete. I'm surprised Microsoft was willing to offer such a premium for Yahoo in the first place. Maybe I underestimate the synergies of the two companies and/or Microsoft's concern about their online division.
The interesting question to me is what comes next...Does Microsoft: A. Sweeten the offer B. Walk away completely C. Give it a year expecting Yahoo's price to drop significantly before making a subsequent offer?
Unless the Yahoo boardmembers have some plan up their sleeves, I expect some very unhappy shareholders should B or C pan out.