Krugman makes some very interesting points concerning how far to trust insurance companies. About THIS far. No really, however far that is on your computer and no farther. They will lie and cheat. Requiring everyone to buy health insurance may give the insurance companies a lot more money from people who will (for the time being) not use the insurance and therefore one could, in a just world, expect the industry to lower costs across the board, but I doubt it (a lot).
However, given the industry's history unless the government forces the industry to lower its' profit margin, they'll just take the money and run with it. Managing these companies profits would be well neigh impossible politically and probably completely impossible practically.
Crook's and Liars point out that it doesn't work that way in Massachusetts. The costs to the individual are still astronomical.