The unchallenged reign of the MacBook Air on the thin-and-light domain is nearing an end -- the Ultrabooks are coming, and the Lenovo U300s looks to be one of the strongest competitors we've yet seen. It's a new entry to the IdeaPad lineup, the thinnest and lightest of a redesigned and reborn U Series that will also include the slightly stockier 13.3-inch U300 and the even bigger but even more serious 14-inch U400. All three are shipping in O