Hi all
Some really good points being raised here!
After my visit here, I'm quite convinced that these are something other than natural markings. Partly, as mentioned before, because these rocks are the ONLY ones in the area of (I'm no geologist, but) exactly the same rock-type. And partly because they look exactly like all the other countless cupmarks I've ever seen! (Although, again - I'm no expert!)
I suspect that most doubts regarding the shape/distribution could be largely due to the erosion. Remember though - this is RIGHT on the edge of a really exposed bit of land in the far west of the Hebrides. And we know what the wind/rain/waves can be like in that neck of the woods!
I've posted a couple more pics from my phone which may help clarify or confound...
http://www.themodernantiquarian.com/post/47296 and
http://www.themodernantiquarian.com/post/47295
G x