I've heard that umbrellas are getting more common for hikers and backpackers-- they are easy to use (as opposed to fighting your poncho or rain suit out of your pack), and are also useful for keeping the sun off.

There are trade-offs, of course, one hand is tied up with the umbrella, and there could be wind/tree limb issues.

I remember reading in an old (80s) Dress for Success book that men weren't supposed to use umbrellas. Better to wear a hat and a raincoat and drag in a half gallon of water, but you look manly!