I've been wearing nothing but MBT's since I first tried them.  I had surgery on my knee a few years ago and find that most regular shoes result in my slamming my heel down first when I walk, making the knee progressively more tender.  With the MBT's this isn't possible.  i don't think it's doing anything for the shape of my legs, as advertised, but it sure is a relief on the knees!  The only reason I don't give it 5 stars is that the soles wear awy fairly rapidly compared to other shoes.  The first time I encountered this phenomenon I figured it was because I was wearing the same shoe, day in and day out.  Then I bought another pair and alternated.  The new pair wore down fairly quickly.  So this time I bought 3 pairs.  We'll see.