Bill Gates opened Tech-Ed 2008 Developers, its annual developers conference in Orlando, Fla., today by saying good-bye to a group the Microsoft founder said has been the company’s most important. “The success of Microsoft really is due to our relationship with developers,” he said in his keynote this morning to a room filled with about 6,000 developers.

It will likely be Gates’ last speech as a full time Microsoft employee; on July 1 he’ll focus most of his efforts on the Bill and Melinda Gates Foundation, which gives away huge sums of the couple’s fortunes to help improve global healthcare and development.

In typical Gates fashion, he spoke of the future direction of application development, which includes continued focus on application modeling. Part of that strategy is project Oslo, the company’s architecture for visually modeling SOA applications and composites. Developers wanting a peek at the platform will have to wait until the Professional Developers Conference in October.

Gates also spoke of services, namely the types of hosted services it needs to play catch-up with against Amazon and archrival Google. “We’re taking everything we do at the server level and saying we have a service that mirrors that exactly. It’s getting us to think about data centers at a scale that we haven’t thought of before…[to create a mega-data center that Microsoft and only a few others will have.”

He also announced that Silverlight 2, beta 2—Microsoft’s media player browser plug-in—was available now, ahead of its “second half of 2008” schedule. He also mentioned that a second beta of Internet Explorer 8 will be available in August.

In what must have been a very light-hearted moment, Gates introduced a Windows-powered robot with Steve Ballmer’s face showing on a monitor where its head should have been. On cue, the robot reportedly threw an egg across the stage and then shouted “developers, developers, developers, developers,” parroting one of Ballmer’s infamous stage rants.