TheStreet. Warren Buffett is arguably the most successful investor of all time. He's amassed an amazingly massive net worth by buying and usually holding stocks for the long haul. Trained under legendary value fund investor Benjamin Graham,

Shares of some of UnitedHealth’s peers got a bump in the wake of Berkshire’s investment in the healthcare giant, and they all look cheaper based on price relative to expected earnings.

Even though Warren Buffett seems to think the value of UnitedHealth stock is about right, that doesn’t mean investors should ignore the long list of unresolved issues facing the company.