Leveraged positions in the stock market jumped 18% in one month and topped $1 trillion for the first time. Increasing use of debt to invest can tell us a lot about investors' attitudes. And while this has always been the case,

Beaten-down UNH is set to challenge its 50-day moving average after a major vote of confidence from the Oracle of Omaha.

Key Takeaways Buffett has long been a big proponent of the index funds that Bogle helped bring to the masses.However, his public declaration that Bogle is an American hero may have also been influenced by the fact that one of Bogle's funds just helped Buffett win a $1 million bet.

Warren Buffett's modus operandi is to wait for price dislocations to present themselves. In a historically pricey stock market, locating value has been virtually impossible. Yet, with UnitedHealth Group stock losing more than half its value since the midpoint of April, a rare price dislocation has emerged.

Buffett owned UnitedHealth shares before selling his stake in 2010, though his Berkshire Hathaway recently acquired shares.

In May, a 13F filing revealed that Berkshire Hathaway was buying mystery stocks. Now, at last, we know what they are.

Warren Buffett is telling investors something -- not through what he has said, but through his actions with the balance sheet of his investment conglomerate Berkshire Hathaway ( BRK.A -0.40%) ( BRK.B 0.83%). These actions should be taken as a warning sign with the stock market reaching elevated valuation levels in recent months.

Berkshire Hathaway's $1.6 billion stake in UnitedHealth Group is helping to lift the Dow Jones Industrial Average to a new record as investors pile into healthcare sector funds.