The jibbitz piggyback was also quite clever:
http://money.cnn.com/2006/11/02/magazines/business2/crocs_si...
The ugliness actually appeals to some people, too.
Other than that, yes they are extremely light and comfortable...
Certain famous websites come to mind. On a tangential point, it seems like these things must be relatively cheap and easily accessible, and cannot become status symbols. Sushi is an example where aesthetic appeal is as important as its palatability. (I'm typing a bit aimlessly)
So, what about those NIKE Naked shoes (or whatever?)? They are less of a fashion statement because they stand out less, I presume?