Updated February 24, 2010 at 10:30 a.m. PST: Updated to reflect that Beta 3 is available again for download.
The short-lived update followed the second, released several weeks ago.
Prior to the SDK being pulled, 9to5Mac managed to gain access and published some screenshots showing an expanded Settings app, evidence of YouTube playing video in HTML5, file sharing, and other features not in previous betas.
Apple's two-week release cycle of this SDK closely mimics iPhone OS 3.0's 2009 release cycle. That OS went through a handful of beta versions before public release. Will the iPad OS follow suit? We look forward to finding out.