Stupid Elf Tricks...

[Carorëiel]

I agree that some of Legolas' stunts are a bit over-the-top, but I think the walking-on-snow thing is held up by the text. In "The Ring Goes South," we get the following:

"Legolas watched them for a while with a smile upon his lips, and then he turned to the others. 'The strongest must seek a way, say you? But I say: let a ploughman plough, but choose an otter for swimming, and for running light over grass and leaf, or over snow--an Elf.'

With that he sprang forth nimbley, and then Frodo noticed as if for the first time, though he had long known it, that the Elf had no boots, but wore only light shoes, as he always did, and his feet made little imprint in the snow."

Granted, the text doesn't actually say that Legolas walks on top of the snow, but I don't think it's too big a leap. I always saw his walking on the snow in the film as a nod to this scene in the book.