To paraphrase the words of our reviewer, ASUS' Zenbook Prime UX31A is the third-best thin and light laptop you can buy. That's high praise indeed when the only two superior devices are the MacBook Air and Samsung's Series 9. So, why does it deserve such love? That's probably down to its sleek design, six-hour battery life and smooth performance. The only things it has in the "demerit" column is a wonky trackpad and weak audio, but we can