Berkshire Hathaway revealed four new investments Thursday in steelmaker Nucor, insurer UnitedHealth and two of the nation's biggest homebuilders — Lennar and DR Horton — but it's not clear if the investments are big enough to ensure that legendary investor Warren Buffett handled them.

The flurry of 13-F filings to the Securities and Exchange Commission revealed that many of the most highly regarded investors were drawn into UnitedHealth in the second quarter.

The "vote of confidence" from Buffett validates UnitedHealth's long-term value, but " (the) management needs to regain trust and credibility with investors, and get back to its beat-and-raise reputat...