I just bought my first pair about two weeks ago and love them too! I have the MBT Walks in black. I hestitated because of the price and the odd look, but now I'd love to get a second pair!
I'm seriously feeling the burn. Not sure if my legs have toned up, but it feels like I'm getting a workout. I live in New York and try to walk home from work in them which is about 1.75 miles. But I have to take MBT "rest" days every once in a while and go back to regular shoes, hopefully I can work up to wearing them every day.