Every quarter, fund managers have to disclose what they've bought and sold. Their latest moves can shine a bright light on smart stock picks.

Today, let's look at investing giant George Soros. Soros is known to some folks these days for his politics and philanthropy, but his fame stems from his wealth, which is a result of his outstanding investing prowess. He founded Soros Fund Management back in 1973, and under its umbrella the Quantum funds racked up an amazing record, reportedly averaging close to 20% annual growth over four decades.

Soros' stock portfolio totaled $4.6 billion in value as of Dec. 31, 2011, down 21% over last quarter. His top three holdings, representing more than 30% of the portfolio's total value, are Motorola Solutions, InterOil, and the agricultural company Adecoagro.

Interesting developments
So what does Mr. Soros' latest 13F filing tell us? Well, for one thing, he's concentrating his holdings much more, having completely sold out of several hundred stocks and ending up with about 145.

Here are a few more interesting details:

Among Soros' new holdings is MELA Sciences (Nasdaq: MELA), which reflects Soros' willingness to buy into very tiny companies. With a market cap recently around $100 million, it's the kind of company that Warren Buffett would typically pass up, deeming it too small to make a difference in a multibillion-dollar portfolio. MELA fans are excited about its melanoma detection device, which recently received FDA approval.

Chinese search engine Baidu.com (Nasdaq: BIDU) got a lot more support from Soros, as the number of its shares held soared 170%. It's still a small holding for the Soros portfolio, but the increase seems to have been wise, as the company recently posted fourth-quarter revenue up 83% over year-ago levels and earnings up 77%. Interestingly, competitor Google is looking to expand in China, while Baidu.com is looking outside it.

Among the holdings that Soros trimmed was biotech concern Elan (NYSE: ELN), which saw its share count drop by 22%. The stock recently took a hit as it posted disappointing revenue, bigger-than-expected losses, and shrinking margins. Still, long-term investors are quite bullish on the prospects for its multiple-sclerosis drug Tysabri, thinking it could be a big blockbuster.

Two of the companies that Soros completely sold out of are Sirius XM Radio (Nasdaq: SIRI) and BioSante Pharmaceuticals (Nasdaq: BPAX). Sirius bears are worried about slowing subscriber growth and price hikes the company is enacting, while bulls point out that recent subscriber growth has been impressive despite price hikes. Rising car sales bode well for Sirius, but at this point, many new car buyers are already Sirius subscribers. BioSante has had some mixed results lately; its LibiGel treatment failed to prove itself (at least so far) a Viagra for women, while its Bio-T-Gel treatment for hypogonadism was approved by the FDA.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13F forms can be great places to find intriguing candidates for our portfolios.

Looking for promising investments? Check out our free special report -- "The Stocks Only the Smartest Investors Are Buying" -- and learn which stocks are appealing to Warren Buffett and other great investors.