I thought this is one thing that Japan will be unable to export to west, as usual, I was wrong.
Check out the below video from Gamespot for Cosplay gathering in London. If only I had known, I would have been there. I certainly would not have worn any costume (You have to stitch it yourself in most cases!) but would have loved to join in the fun.
Gaming Today video
Unfortunately, the Cosplay video is half way through this video. Here are the pics at Gamespot.