Does anyone have or has heard of the MBT shoes?

They are supposed to help you walk in a new way to engage more muscles in your legs and make you work harder to walk....

Does anyone have a pair of these? Are they worth shelling out the $ for?

I've never heard of them, but it doesn't sound like a good idea; to me it sounds like the type of equipment that could mess up your body. Your body doesn't need special shoes to "engage more muscles." If you're working out (even walking) at your maximum capacity with proper form, your body will get strong and proportioned on its own.
Also, if you want walking to be harder, try jogging...

It is TRUE that to walk barefoot or to walk on uneven surface harder, engage more muscles than to walk on even surface in nice shoes.

BUT why does anybody need $250 shoes to achieve all these, when those goals can be achieved FREE by walking barefoot OR on uneven surface, trail etc. Even more simple: try tree pose. (See this link for example.) It gives you exactly the same "more muscle engaging effect" as MBL. It is very good for your posture as well as strenghtening your arch/ankle. You can do it while watching tv.

(In a sporting good store I tried those miracle shoes, and I walk/run a lot on trail, so I have some base for comparision.)

P.S.: If you want to make your walk REALLY hard try mud walking. It will engage all your muscles from toe the neck.

Cheers: Eva