I have one. Got it a month or two ago. It's nice but nothing spectacular. It's another interesting lens effect, like using a macro or shallow DOF. I don't really see much difference on my Pentax body from using one on a Canon body. Its about the same. Getting the lens off my K10D is a little trouble because there's very little to grab onto at the base of the lens but it doesn't prevent lens changes or anything like that. Just a little more effort is involved.
I have a very few images here:
lensbaby Photo Gallery by alinla at pbase.com