Analyst Upgrades

• General Growth (GGP) to outperform from neutral at Credit Suisse.
• PPL Corp. (PPL) to outperform from market perform at FBR Capital.
• Hudson City Bancorp (HCBK) to neutral from reduce at Nomura.
• Hologic (HOLX) to conviction buy from buy at Goldman.
• Cognex (CGNX) to overweight from neutral at Piper Jaffray.
• Buckeye Partners (BPL) to outperform from market perform at Wells Fargo.
• Ericsson (ERIC) and Health Care REIT (HCN) to buy from neutral and Olin (OLN) to neutral from sell at UBS.
• Nalco (NLC) to overweight from neutral at JPMorgan.
• Watts Water (WTS) to buy from hold at BB&T.
• McDermott (MDR) to buy from neutral at Pritchard.

The past week's data-point-of-consequence for investors had to be investment decisions by Warren Buffett's Berkshire Hathaway (BRK.A).

Buffett ended positions in several stocks in the fourth quarter, including the Bank of America (BAC), Nike (NKE), Fiserv (FISV), Becton Dickinson (BDX), Comcast Corp. (CMCSA), Lowe's Co.s (LOW), Nalco (NLC) and Nestle (NSRGY), according to a filing, The Wall Street Journal reported.

Berkshire added to a holding of only one stock in the fourth quarter: Wells Fargo (WFC).

Analyst Upgrades

• Athenahealth (ATHN), Ensco (ESV), Pride International (PDE) and Sinclair Broadcast (SBGI) to outperform from market perform at Wells Fargo.
• CIRCOR (CIR) to buy from hold at BB&T.
• Urban Outfitters (URBN) to hold from sell at Citigroup.
• Shaw Group (SHAW) to buy from neutral at UBS.
• MGM Resorts (MGM) and Boyd Gaming (BYD) to buy from neutral, as well as Intrepid Potash (IPI) to neutral from underperform, at BofA/Merrill.
• Carlisle (CSL) to buy from neutral at SunTrust.

"Warren Buffett's Berkshire Hathaway revealed a new position in Nalco Holding (NYSE: NLC); it's my favorite pure play on water filtration," says Chris Mayer in Daily Wealth.

"With a $1.6 billion market cap, Nalco is a small-cap stock, but it's actually one of the world's largest water-treatment companies. Customers use Nalco's products and services to prevent corrosion, contamination, and the buildup of harmful deposits.

"Buffett picked up 8.7 million shares. That makes Berkshire the second-largest shareholder in the company, with a little more than 6% of the shares.It's easy to see what Buffett likes.

Suppose you have a wildly successful business in an ultra hot market. Time to sell?It's probably something to consider. Well, that's certainly the state of affairs in the private equity world.

According to the Wall Street Journal, the founder of Apollo Management LP, Leon Black, is mulling these kinds of cash-out issues [subscription required]. His private equity firm is one of the largest and has done deals such as for Harrah's Entertainment Inc. (NYSE: HET), Realogy Corp. (NYSE: H), and Nalco Holding Co. (NYSE: NLC).

Based on the market multiples -- such as for Fortress Investment Group LLC (NYSE: FIG) -- it looks like he can take home about $1.5 billion selling a minority stake of 10% but still keeping control of his destiny. To me, this is having your cake and eating it too.

What's more, by selling the stake to private investors, there's no need to go through the hassles of the IPO process. In other words, Black has more time to do deals. Although, if the Apollo stock is registered – which is likely to happen – it will become publicly traded within the year.

It's an interesting structure and is typical for small companies. As for Black, he does think out of the box and the back-door IPO does make a lot of sense.

Tom Taulli is the author of various books, including the Complete M&A Handbook and the EDGAR-Online Guide to Decoding Financial Statements.