Microsoft opened its now-annual BUILD developer conference this week under raining skies at its corporate headquarters in Redmond, Washington. And though hosting such an event at the ill-equipped Microsoft campus might have been a mistake, there’s no doubt that the developers here are pumped about the software giant’s latest platforms.

In a freewheeling keynote on Tuesday, Microsoft CEO Steve Ballmer, Windows Phone Director Kevin Gallo, and Corporate Vice President Steve Guggenheimer were present, with Ballmer discussing Windows 8, Gallo discussing Windows Phone 8, and Guggenheimer explaining how these new platforms represent one of the biggest developer opportunities on Earth.

Ballmer’s segments were particularly good, with a natural and unforced walkthrough of Windows 8 using his own personal configurations. It was clear that Mr. Ballmer not only knew Windows 8 well, but that he was using his own data. It made for the most compelling Microsoft keynote presentation in years.

But BUILD, of course, is a developer show.

“The developer opportunity on Windows has never been greater,” Guggenheimer wrote in a post to the Official Microsoft Blog. “It’s easy to publish to the Windows Store, and Microsoft offers the most developer-friendly revenue-sharing terms on the market.”

Microsoft released the eagerly anticipated Windows Phone 8 SDK on Monday, as well, giving developers their first chance to write apps that target unique features in the new platform. (The Windows 8 developer tools have been available since September.) The firm also touched on how developers can share code between the two platforms, though it’s not possible to write a single app that runs on both.

One interesting note about BUILD: For all the controversy online about the firm’s decision to base all of its products around a design language (formerly called Metro) that relies heavily on multi-touch and other natural user interfaces, the size and enthusiasm of the crowd here suggests that Microsoft is on to something. With BUILD 2012, everyone here knew exactly what they were getting into, and this show sold out in under an hour. The developers here are excited for the future and eager to learn more.

Microsoft also energized the crowd by announcing a series of exciting giveaways for paid attendees, each of whom received a Surface with Windows RT 32GB tablet, a Nokia Lumia 920 smartphone, and 100GB of free SkyDrive cloud storage. Not bad for the first day of the show.

On the flipside, attendees were rightfully outraged by the long lines, many of which were forced to string along outside in the rain next to unused tents. Microsoft’s campus simply can’t adequately host the thousands of attendees that are present at the show, and Mr. Ballmer hinted this would be the last time it attempted such a thing.

More soon….