Coolant light would go on intermittently for a few days. Had coolant topped off. Then the next day the car overheated unexpectedly and quickly while on the highway. Drove to gas station. Filled coolant. Coolant was not leaking with car turned off. Turned on car to drive home, and 20 miles later all the coolant was gone. Found similar problems reported on this website. Took it to a trusted mechanic.

Repair needed: replace upper and lower manifold gaskets & seals, replace thermostat, change oil and filter. Repair cost nearly $800. If coolant got into the engine (which happens in some cases with this design flaw), this could have been much, much worse.

Turns out GM lost a class action law suit because of this problem: http://www.girardgibbs.com/dexcool.html

I've owned two GM cars and had terrible experiences with both. I won't be buying one in the future, and their fancy new ad campaigns don't fool me either.