We can't wait for Danny Boyle's Sunshine to come out on DVD next Tuesday. Sunshine might have been the best SF movie of 2007, even though its science was iffy in places. Take this cool-looking scene, where hapless communications officer Harvey tries to jump from one spaceship to another without a suit and doesn't quite make it. Within a minute or so, he freezes and becomes so brittle his arm shatters like an icicle. What would actually happen to an unprotected Harvey in space?
Basically, Harvey would die of asphyxiation. He would quickly get "the bends" because the air in his lungs would be trying to escape, and hypoxemia would result. He wouldn't explode, because his skin is actually strong enough to hold everything together even in vacuum. But he also wouldn't suddenly turn into a freeze-dried popsicle, like he does here. It takes time for your body temperature to equalize with the near-absolute zero of space.
NASA knows a lot about what would happen to unshielded humans in vacuum, because of an accident in 1965 where a poor guy's suit ruptured in a vacuum test. He lost consciousness quickly but was otherwise unharmed. There's also the experience of the poor chimpanzees (PDF) whom scientists exposed to a vacuum back in 1964.