MikroKopter - HexaKopter- 6 propellor - GPS guided
I had to bookmark this for future reference - Its stability and build impressed me, so did its GPS navigation and fear of heights
I think in this case more propellers give redundancy. If one (or maybe even more) motor fails you might still be able to land without crashing. I'm not a copter-expert so I might be completely wrong. But I do know there's octocopters too (http://www.google.com/search?q=octocopter) and I've heard that octocopters can be used to take aerial photos easily (and to earn some easy money by doing that).
Edit: And more motors give you more lift too. That could be nice if you want to lift SLR camera for example :-) A friend of mine sent me a link about octocopters and aerial photography some months back but I've seem to have lost it :-(
pointless robots are the best
Some acceleration! Video is lacking music.
Just turn up the volume and enjoy the "The bee swarming sound"
Even with a 1Kg coke bottle the acceleration is impressing - but i was dissapointed that he did not test the true payload limits........