Have you done one? I see there was one in Chicago, and Portland. Big one in London. I wonder how they got around the public decency laws, at least I thought there was one to prevent indecent exposure. Also would think it's uncomfortable.
I was at a wedding reception at some kind of summer resort and they had some loaner bikes for the guests in various states of disrepair. I got a report in the morning that apparently I was seen riding a tireless bike in the buff while racing a couple of cousins who were also nude on a tandem.
I don't know if I was comfortable, but my knee was pretty skinned up the next day and I had a wicked hangover.