On top of Buffett's visit to the White House where he, along with George H.W. Bush, Maya Angelou and others were honored by President Obama and presented with the Presidential Medal of Freedom, the Berkshire Hathaway ( BRK.A) 13f filing was released to the public. Commentators, analysts and others have spent the week fiercely digging through the document in hopes of uncovering clues regarding Buffett's view of the global marketplace. In the final months of 2010, Buffett made a number of tweaks to his legendary portfolio. Overall, the famously bullish investor ended the quarter as a net seller, unloading shares of a number of his holdings and further increasing the size of his already substantial pile of cash. Bank of America ( BAC), Nike ( NKE), Comcast ( CMSCA), Lowes ( LOW), Finserv ( FISV) and Nalco ( NLC) were among the biggest victims of Buffett's trimming. Over the course of this quarter these positions were closed out completely. Buffett's portfolio cuts have received the lion's share of the attention from investors and market commentators throughout this past week. However, the famous investors made some purchases as well. The investor's second largest holding, Wells Fargo ( WFC), received a vote of confidence when Buffett added 6.2 million shares to his already sizeable stake. Wells now accounts for 20% Berkshire Hathaway's investment portfolio. This past quarter's action highlights the conservative shift and streamlining taking place within Buffett's investment portfolio. As I've explained in the past, due to the size of Berkshire Hathaway, Buffett can no longer expect to score big profits by investing in small, fast moving companies. Instead, he must rely on the long-term stable returns that result from owning large and mega-cap companies. For the start of 2011, this strategy has proved successful. Improving economic conditions have been beneficial for many large, quality companies. As a result some of the biggest names underlying the Berkshire umbrella have also become some of the portfolio's strongest movers. According to a report from Bespoke, two standout performers in Buffett's portfolio right now are energy goliath, Exxon Mobil ( XOM) and U.S. conglomerate, General Electric ( GE). As of Feb. 16, year to date, these two companies are up 15% and 17%, respectively.