Nope, not me.

Keens I guess would be ok as they do offer some protection, but on the trails I ride (technical, rocky singletrack) there's just no way I'm taking that risk. I knocked my pedal or foot no less than 5 times yesterday, once hard enough to dislodge a sizable rock and send it tumbling down the embankment.

I'd consider them for fireroad type riding and certainly commuting but not serious mountain biking.