Than road bike calipers maybe not (but there's also significan aerodynamic concerns there. But compared to a V-brake setup they're lighter.

I don't disagree that spuds are the best for ultimate pedalling efficiency, but they simply don't fit into my kind of riding. The other day I was on top of the pennines, and slogging it polaris-style across the moors. I perfected the technique of riding as far as possible with momentum into the mud puddle, then jumping for it, which would be kind of difficult with spds. A pair of stiff-soled shoes and good pedalling technique (ball of foot, spin, pull up on the way up (it can be done with platforms, just as bunnyhopping can) gets you most of the way there though, and close enough for me. My racing days are over (best result 14th in XC, 3rd in Dual Slalom) so I'll stick with these (which are light, as they're alu rather than steel caged. Paid for by the winnings from dual slalom...).