Everytime I see someone misuse lose/loose, it makes me want to kill them with knives. It's important to be precise, you can't just work everything out from context!
English has the most moddy grammar of all languages, with so many exceptions and shit - this is one of the things I hope disappear as the world embraces English.
Which doesn't cover every case I can think of, but demonstrates the difference. Also lose is a verb, loose is (almost always) an adjective.