Personally, I find the circles raaather obnoxious.

I don't know about you guys, but my attention tends to be instinctively drawn towards things that move and things that are bright, something I'm probably not all alone with, considering modern age advertisements like to use bright flashing lights to draw attention and most games darken skills on cooldown.

That said, I'm okay with circles on principle - but make them dark circles. As it is, skills on cooldown draw more innate attention than skills that aren't and that is, uh...a little bittle counterintuitive.