Ok although one book (an English history book that I would not think was that popular) kept selling out from the various sellers listed within a minute of my selecting it. Nothing your site can do, of course, just odd and slightly annoying.
Also, in using your site in the last month, my cart often disappears and the items I've selected are then unavailable for a day. It would be nice to have my cart saved for more than a couple of minutes when I'm logged in.