Netbooks are selling at a nice clip -- IDC predicts more than 20 million units sold by year's end -- as consumers and education buyers wolf up these streamlined, low-cost laptop alternatives. Next up: the enterprise. Netbooks is a "category with legs," says Stephen O'Grady, an analyst with Seattle-based consultancy RedMonk, pointing to recent market activity as an indicator of the netbook's viability. Most obvious, he says, is Google's decision to build a separate Linux-based operating system -- Chrome OS -- specifically for netbooks. Meantime, Microsoft is grappling with "hard questions about its OS pricing relative to netbooks," and virtually every major hardware maker, apart from Apple Inc., has an offering in the category.