Richard Hogland was on Coast-to-Coast AM last night saying exactly this. There is a problem in one fuel cell's coolant circulation pump motor, and if they lose a fuel cell they have to come home. He can't believe they're even attempting to launch, given that if they do make it to orbit and the fuel cell dies, they will have to jetison the ISS beam payload. The Shuttle is too heavy to return with it in the cargo hold.
Good. I got nervous when Wayne Hale said it was "probably acceptable" to launch.
Probably acceptable???
I highly recommend reading Mike Mullane's autobiography Riding Rockets: The Outrageous Tales of a Space Shuttle Astronaut
Great behind-the-scenes look at Shuttle era astronauts.
I was glad that the astronaut office voted no on the launch because they've had to be silent for so long. Astonauts have been reluctant to speak out for fear of being "blacklisted" and lose their chance to fly. Mullane goes into good detail about this.