I didn't even notice the serif font, because I have overridden the font-family in almost all places to the Ubuntu font-family (hooray for user style sheets!). I tried it as an experiment somewhere around a year ago. I strike the occasional website that doesn't look right and where it looks like the typeface used may have damaged it, but overall, it's marvellous. I noticed very quickly that the whole web was prettier and more readable. I tried going back, just out of curiosity, a month or two later. I went back to overriding the font-family less than a week later.

But as far as their layout is concerned, I do like the large typography, and don't see any problem with the paragraph spacing and layout. Overall, it's a nice, clean layout.