After an ammonia leak was discovered on the International Space Station last night, NASA and the ISS crew are working together to come up with a fix. It's been decided that an emergency spacewalk will be conducted to inspect the leak and attempt to fix it before matters get worse. The leak is on the outside, so it isn't immediately life-threatening, but the supply will run out if the leak continues.
The ISS's power relies on ammonia coolant, so if that supply runs out, the space station would go dark and all the vital equipment needed for survival would stop working, which at that point the crew would be in grave danger. According to ISS Commander Chris Hadfield, the leak appears to have been stabilized, but there still needs to be a solid fix.
In order for the ammonia-based coolant system to operate normally, it needs a certain amount of ammonia in the tanks. However, based on the rate of the leak, the levels in the tanks could drop below that sweet-spot level within 48 hours, at which point the system would be at risk of shutting itself down due to a lack of ammonia. Of course, the station can operate on a broken cooling system, but it would take some clever thinking to prevent ISS components from overheating.
Luckily, the astronauts on board are fairly confident as far as where the leak is coming from, so once they begin their spacewalk, they'll hopefully be able to go right to the leak and immediately begin repairing it. The spacewalk is being planned as we speak (with a live stream of the whole thing), and astronauts Chris Cassidy and Tom Marshburn are getting their spacesuits prepared for the spacewalk, which will take place at some point tomorrow.
In a similar but unrelated note, the United States Alliance has switched over the ISS's computer systems from Windows to Linux to make sure that they're "stable and reliable." Specifically, the ISS was running Windows XP (not even Windows 7?), and they have now started to switch to Debian 6. For what it's worth, however, some computers on the ISS have already been running various versions of Linux, including RedHat and Scientific Linux.