It's silly: most companies did not have their best year ever in 2009. NRG did, and they are being punished because it looks like they are shrinking moving into 2010. Hardly, just compare 2010 to 2008, which was their best year ever until 2009. 2008 is a nice comparison because Buffett bought in back then, at a price of around $40-$45.

At an asset level, NRG has about a billion dollars more cash, RRI retail, and a few new power plants.

On an earnings level, EBITDA guidance is identical to guidance going into 2008: $2.2 billion. Their guidance for free cash flow is also almost identical: about a billion.

On a cash basis, they have $2.5Bn in cash, and $1Bn in recurring FCF, so if they didn't spend any of that money, in less than 4 years the current market cap will be available in cash.

In short, you have a company with the same earnings outlook as when Buffett bought 2 years ago, only now it has a billion dollars more cash, an entire large new business unit, a lower share count, and you're paying a price that's a bit more than half of back then. I can't name any other companies that have done so well over the last 2 years, and have been punished so harshly (but if someone names one, I'll probably buy it).