It seems slightly odd to call it "leaner" when you're adding stuff on top of CSS. The additions seem nice enough, but to me, "leaner" means that the number of [mis]features is being reduced to make a smaller spec and implementation.
Yes. And to me it seemed odd that 3/4 of the examples of LESS actually require MORE typing than the CSS. So perhaps not the best name, but looks like a nice tool.
Or maybe LESS should be an acronym: Less Equals Simpler Styles :-)