Crank Brothers offer both a "road" and a standard cleat. The road one has pontoons on the sides and is supposed to help you walk, and the pontoons hook up with the Quattro pedal's sides to provide a larger platform. Some shoes will have bolt patter issues with the 2-bolt system, and others may find it hard to walk on a smooth road shoe with a bit of metal underfoot.

I use Adidas's Adistar XC shoes, which are under 400grams with the Egg Beater cleats. I've got them on my mountain, cross, and road bikes, with one pair of shoes. Best decision ever. With their carbon soles, I don't even pretend to understand what a "larger platform" would do for me - it feels solid with no pressure points and just enough float as-is.

@ guts2tri - why spend $120 on beaters when you can get them for less than $80 barely looking around? It's a bargain.