If you were thinking about heading to Microsoft's BUild 2013 conference and didn't already pull the registration trigger, you waited a little too long.

Registration opened for the conference at 9 am PDT on April 2. By 12 noon PDT, a message was on the site advising those attempting to register they'd be put on a wait list.

Update: Around 1:30 pm PDT, @kimtiede told me the Build site was no longer showing that the conference was sold out. So maybe there's still hope for those who wanted to get in.

Here's the page I saw at 12 noon PDT:

That page is no longer displaying as of 1:30 pm PDT. Instead the site seemingly is allowing new registrants to apply.

Microsoft officials declined to say how many attendees they'll be allowing into the conference. (I asked.)

Build 2013 is happening from June 26 to June 28 in San Francisco. In addition to talking about Windows client, Microsoft speakers also will be discussing Windows Azure, Windows Phone, Visual Studio and Xbox at the confab.

Last year, Microsoft's Build 2012 conference sold out in under an hour . There were limited spots available because Microsoft opted to hold last year's event on campus. Many of those who were put on the wait list ended up getting into the 2012 event, however.

Microsoft officials have not posted detailed agenda topics yet, but according to one tweet I saw, that will be happening shortly before the conference begins.

Microsoft's Windows Blue, a k a Windows 8.1 , is expected to be a big topic at the show. Given leaks about the expected Blue roadmap, Microsoft could distribute either the internal second milestone build (upon which its developers are working now) or the one-and-only expected public preview test build of Blue at the event. As far as hardware giveaways, it sure seems like Build 2013 would be a good time for a smaller Windows 8 tablet to make its debut....

Update (April 3): Microsoft officials posted a tweet around 8 am PDT today saying that Build 2013 is officially sold out. The keynotes and select sessions will be Webcast, however, as they were for previous Builds.