Mavericks locked up on me twice lately and in both cases the screen just froze rendering mouse, keyboard and trackpad unresponsive. The first time that happened I was video conferencing with a co-worker using Fuzebox. Interestingly he could still hear me and I could hear him, so the system didn’t crash completely. At the time I was using a 2012 MacBook Pro with Retina Display connected to a Cinema Display. The second time I was working with FinalCut Pro and Aperture using a late 2013 MacBook Pro with Retina Display and the same Cinema Display.
I had similar problems before under Mountain Lion and my workaround back then was to SSH into my MacBook Pro and to shut the system down from the command line. The issue in Mountain Lion was finally fixed when Apple released 10.8.3. This time around I hope for a quicker fix and the seed notes of the latest 10.9.1 seed, asking developers to focus on Graphics Drives, among other things look promising!