You may have noticed this screen when you connect your Zune to a second PC: You might not know this, but guest sync is my favorite thing about Zune. It’s not really something we called out in advertising or in PR, but for a music geek it’s a really cool feature. After talking to the program manager responsible for guest sync, here's what I found out: You can take your Zune device, and sync it with multiple PCs - via guest sync. While you’re in guest mode, you can add content, manage your library...