The world's biggest online retailer has poached an executive from the world's biggest software company - and that's an indication that the two are competing more closely than you'd think. Brian Valentine, a Microsoft executive left without a specific assignment in a recent reorganization of the Windows group, is joining Amazon.com as a senior vice president, the Seattle Post-Intelligencer reports. While Amazon is mum about Valentine's new duties, the company has been increasing its spending on technology and has been building services like online storage and grid computing on top of which startups can build and run software - an initiative that competes directly with Microsoft's Windows franchise.

Valentine is just the latest in a wave of Microsoft executives to leave - and he's not even the first to leave for an online retailer. David Risher, a key early executive at Amazon, was a product marketer at Microsoft. But the new wave of defections at Microsoft is hitting closer to home. Instead of losing marketers, Microsoft is losing evangelists like Vic Gundotra, now at Google, and inspirational engineering managers like Valentine. What's worse, Gundotra and Valentine could be helping build Web computing platforms that undermine Windows. That's the kind of brain drain that really sucks.