It used to be that "convertible PC" could mean only one thing: a laptop whose display swiveled around, folding down into tablet mode. Now that Windows 8 is here, though, the category has become a bit muddied. How else to describe our recent collection of reviews? In just the past few weeks alone, we've tested a laptop whose screen folds all the way back, an Ultrabook whose display flips inside the hinge and yet another with a slide-out keyboard. Anything goes -- at least until consumers decide which form factor they like best. But when Lenovo calls its new ThinkPad Twist a convertible, you can rest assured it's using the old-school definition. As the name implies, it has a rotating screen that allows it to be used
