Top value investor Whitney Tilson says that we’re in unusually uncertain times, and that he’s playing defense with his portfolio.

“We believe that we are in a period of ‘unusual uncertainty'”, Tilson says in a lengthy presentation that also includes a good deal of information about behavioral finance and the biases that investors are prone to. “The most likely scenario is neither a boom nor bust but rather ‘muddling along’ for 2-7 more years.” (A tip of the cap to ZeroHedge.com for highlighting the presentation, which is available on Scribd.com.)

A year ago, Tilson says, he was on the offensive in terms of investing. “Now,” he says, “we’re playing defense, as we trim both our long and short exposure and shift our longs toward large, dominant, cash-rich companies.”

Tilson focuses on two of those large, dominant companies in particular: Microsoft and Berkshire Hathaway, both of which he’s especially high on. On the short side, he’s finding an opportunity in SalesForce.com, which he categorizes as a “momentum stock priced for perfection”.