As quick as Lenovo has been to hop on the Ultrabook bandwagon, it hasn't been so eager to launch big-screened models. Its new ThinkPad S531 explores that territory at last: the Windows 8 PC mates a slim profile with both a 15.6-inch, lay-flat LCD and a large keyboard. The experience will otherwise be familiar to those who've seen the S431, as it shares the same basic design language, the
