Just saw in a movie, a guy jumped off a building using a lawn umbrella as a parachute. Would that work in reality?
The science entertainment television show, MythBusters, investigated this claim in their 18th episode (in the 2004 season).
Wikipedia summarised their findings:
Opening an umbrella will slow a fall from a building enough to make it survivable: Busted
Though different umbrellas did slow a fall, the impact was still deadly. A real parachute was also tested but found to be unable to properly arrest a fall from only 60 feet (18 m). The best an umbrella can do is hold the person somewhat upright, causing less damage to the head.
The MythBusters team do an excellent job of promoting the concepts of testing claims through experiment, but they cannot be considered the most rigorous of scientific investigators. However, for a claim of this level of unimportance, it seems a sufficient level of evidence. If you were planning to risk your life jumping off buildings with just an umbrella, I would urge further experimentation!