Pfft! While they do indeed look quite good fun, being a somewhat round figure (I'm not fat, just short for my weight) I cannot begin to imagine using them. Not only would I resemble an upside-down Weeble, but as the bit that make contact with the ground is so small in terms of surface area, I can just see my weight pushing it into the ground like a drawing pin, leaving me standing on my feet, but riveted to the ground with 12" of spike. :)
I was wondering where these came from you see everyone using them in a finance company advert Zurich I think it is. And as for you link SANTOS7 brilliant, I was kind of expecting the guy to be blown into little pieces. What some people will do for fun eh.