One thing I miss from GR is the preview of the blurb of a book when you hover over the title/cover. You can see the first 100 or so characters of the description when hovering the mouse. (I've recently moved over from GoodReads - love it here!)

So you can get an idea of a book without having to click through to it, which given that SG sometimes loses my place if I click through and then use the back button to return to the results list would be really handy.