While the "vote of confidence" from Buffett's investment validates the long-term value of UnitedHealth shares, the "management needs to regain trust and credibility with investors, and get back to its beat and raise reputation of the past," said James Harlow, senior vice president at Novare Capital Management.

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 only one of the investments was big enough to ensure that legendary investor Warren Buffett may have handled them.