It's the eternal question of the rule maker investor: At what point does a company's market dominance, its ability to set the rules of the game, begin to breed arrogance in the company -- and contempt among its customers?

A new report summarized in The Wall Street Journal this morning suggests that mega-insurer and dual Motley Fool Inside Value / Motley Fool Stock Advisor recommendation UnitedHealth Group (NYSE:UNH) may be reaching that point. According to an opinion survey covering doctors' satisfaction with 130 of the nation's largest health plans, UHG ranked dead last within the subset of the nation's seven largest national insurers based on its ultra-slow willingness to pay claims filed by doctors treating its clients. The survey used six main criteria, plus overall satisfaction.

UHG's assertion that it "resolves" 95% of its claims within 10 days and "pays its bills promptly" notwithstanding, survey conductor Athenahealth Inc. reports that UHG's average time to payment of 38.3 days ranked worst of the seven largest insurers with nationwide reach. (Note: when payment tardiness is blended with other aspects of the company's performance, UHG moves up two places to fifth place out of seven.) Ranked from best to worst, the fastest payers are Aetna (NYSE:AET) at 29.8 days to payment, Humana (NYSE:HUM), Cigna (NYSE:CI), Medicare, WellPoint (NYSE:WLP), and fellow Stock Advisor pick Coventry (NYSE:CVH) hovering just above UHC at sixth place.

Is this good, or bad? I suppose it depends on your perspective. If you're UnitedHealth Group, or a medium-term investor in same, you probably like this news because it provides quantifiable evidence of the insurer's pricing power -- its ability to make its "suppliers" wait for payment until it's good and ready to cut a check. Simply put, the longer you can make customers twiddle their thumbs, the longer their money generates interest for you. (For more on the concept, called "days payment outstanding" in industry parlance, check out fellow Fool Rich Duprey's March column "4 Stocks That Make Fast Cash".)

That said, I do see a longer-term risk to UHG here. It may be milking its customers for all they're worth today, but the longer it does so, the closer we come to the day when the cows refuse further milking, and begin to turn down customers carrying UHG insurance cards (such as yours Fool-y, by the way.) That, my friends, will not be good for business.

Meanwhile, how are UnitedHealth's numbers holding up? Find out in:

And for a full body scan of the firm's investability, don't forget to pick up free copies of Motley Fool Inside Value and Motley Fool Stock Advisor in the waiting room.

Fool contributor Rich Smith owns shares of UnitedHealth Group. The Motley Fool has a disclosure policy that never makes you wait. Click here.