Monthem, canyoning in Australia is very different to in Europe. The water here is generally warmer, as is the air temperature, so it is safer. There are many canyons here that I still wouldn't attempt in the nude, because they are very long, very cold or require lots of abseils (the slower you move, the colder you get). I think if you pick the right ones, even in Europe, it could be fun.
Stuart, you are right about the rocks usually being smoother in the creeks. I actually kept my shoes on for this one (I included it in essential safety gear like the helmet and harness) but I think you could lose them without much trouble. You actually get more control with bare feet as you can feel the rock so intimately.
AElf, you should totally do a road trip to Utah some time for some proper canyons! Our canyons are similar, in that they are cut deep through a sandstone plateau, but are much moister. In fact, where US canyons are bare and rocky, ours are filled with moss and ferns, so are usually a sea of green.
Oh, yeah, if you flip upside down to rappel you end up holding the rope at arm's length below (above?) your head. It keeps it away from you and makes a great photo!
Advent, that sounds very cool. I'll have to give it a go. The photos would be crazy!
Karla, you and Stuart should definitely plan to do it again as a couple, but this time nude! I'd love to hear the stories if you do make it happen!!!