OK, another report.  First, when it locks up, there is no ssh access possible;
it doesn't even ping.  

Second, I've narrowed it down this far:

Working: kernel-debug-3.6.11-3.fc18.x86_64
Not working: config-3.7.0-0.rc0.git2.4.fc19.x86_64

Those kernel version numbers are the RPM packages that I installed.  

Third, I grabbed a copy of the dmesg messages on the working kernel, so that we
can see what happened immediately after the place where the crash was
introduced.  These may also be enlightening.  I'll attach them.