Long-term growth stock expert Alexander Green sees long-term upside potential for conservative investors willing to invest along side of Warren Buffett.

Here, the investment director of The Oxford Club reviews Berkshire Hathaway (NYSE: BRK.B), a holding in his model portfolio.

"The market surprised investors with the magnitude of its drop over the last year and a half. Then it surprised them again with a furious rally that began in early March.

"What lies just ahead? No one knows for sure, of course. But we do know several investments that are attractively priced at current levels, such as Berkshire Hathaway (BRK.B), a conservative choice, run by investment great Warren Buffett.

"Stocks, by just about every long-term valuation measure, are undervalued," says John Reese, who continues to recommend putting money to work in undervalued stocks.

In his Validea newsletter, he selects "undervalued" issues by using screens based on the investment strategies of leading investors such as Peter Lynch, Ben Graham and Warren Buffett. Here's a a look at four current buys in the oil sector.

Reese explains, "If you think you can predict investors' emotional states, or how an unprecedented economic crisis will play out, then go ahead and wait for the bottom. I suffer no such delusions, however.

"Rather than playing the risky game of bottom-calling -- which more often than not leads to investors missing the big initial push of a new bull run -- I'll continue to put money into undervalued stocks.

"Though the past year has been tough for Warren Buffett, we still like Berkshire Hathaway (NYSE: BRK.B), which we believe is well-positioned for the year ahead," says Paul Tracy.

In his StreetAuthority Market Advisor, he looks at the holding company which is a position in his "undervalued gems" model portfolio. Here's his review.

"For only the second time in the investment-based company's 44 years, Buffett saw the book value of Berkshire drop. Of course his book value decline of 9.6% should be put in context with the 37% loss incurred by the S&P 500.

In what surely must be the PR move of the decade, Moody's Corp. (NYSE: MCO) has downgraded Berkshire Hathaway (NYSE: BRK.A) from AAA to AA2.

Why is this a great PR move? Well, Berkshire owns 20% of Moody's. And what could be a better demonstration of Moody's independence and objectivity than its decision to downgrade the financial strength of its biggest shareholder?

Pretty clever, no? Sure -- unless you start to consider that Moody's and the other ratings agencies gorged on fees from investment banks to rate toxic waste for years -- using their AAA credit ratings to convince investors to buy the securities. Now that the ratings agencies have no fees to earn from rating toxic waste, they are studiously trying to rebuild their reputation for objectivity.

In the investment banking world, it's important to cultivate key relationships with powerful people. It is a way to riches.

This has certainly been the case with Byron Trott, a top Goldman Sachs (NYSE: GS) banker. His top client? Warren Buffett.

Well, it appears that Trott has decided to leave Goldman (keep in mind that Trott has been with the firm since the early 1980s). That is, he will now operate his own merchant bank. In fact, he plans to raise as much as $2 billion for a fund.

Heading into the week's end, we find that the ground under Wall Street has shifted a little. For at least one week this year, investors have looked at the glass as half full, lending some support to a story I posted earlier in the week: Is the stock market spring loaded? Could it move 3,000 points higher now?

Given that there was plenty of bad news, and some of the good news was suspect, I think investors simply decided "it is better to light one small candle than curse the darkness."

"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.

• "And the American people are simply apathetically sitting back while our CORRUPT Congress who enabled and allowed all of the corporate FRAUDS, continues to allow the CORRUPT CEOs and Boards of Directors run those corporations, and to keep their ill gotten "weath" that they amassed while mismanaging the corporations, and orchestrating and perpetuating all of those FRAUDS."