In less than five months, on Oct. 1, the Affordable Care Act's insurance exchanges will go live online. Millions of Americans will suddenly be able to log on to a website and choose their own heath-care coverage from a menu of subsidized options for prices and coverage levels. As the opening day gets closer, anxiety is increasing over how well these online exchanges will function.

Seventeen states and the District of Columbia are operating their own exchanges, seven states are operating exchanges in partnership with the federal...