They might look a bit strange (a bit like I have Hobbit feet), but they're actually extremely comfortable. The sole is thin enough that it's almost like walking barefoot - you can actually feel the difference in texture on the ground - yet the sole is also thick enough to offer decent protection while walking over stuff that would be a bit painful or dangerous barefoot.
It takes a bit getting used to putting them on. The first time I tried, I had no sense of where my toes were - I had to feel them with my hand to figure out whether they were in the right toe slots. It was a good eye opening experience revealing just how much lack of awareness I have with that part of my body. Now that I've worn them a few times, it's definitely easier to put them on properly.
Vibram originally designed these things as water shoes, but they've been adapted for all different kinds of activities. I bought them because I think they'll be useful for practicing karate outdoors. Having the individual toe movement gives a much better feel than wearing shoes. People even use them for training while running, although since you need to run differently (more on the balls of your feet), it's recommended that you don't do really long distance runs starting off.
I recently wore them on an hour long hike through the woods and they were ok. It's definitely easier in regular shoes or boots, but it gave a nice carefree barefoot feel. I did need to pay a bit more attention to where I was stepping - stones and roots hitting the sole of the foot unexpectedly was still a bit uncomfortable. I definitely wouldn't recommend wearing them with a big pack on your back - there's absolutely no ankle support.
I even wore these shoes to work once, although I did change into regular shoes half-way through the day. They were bringing a bit too much attention. The folks at work weren't ready for my forward thinking.