This entry is quite simple: don't use SMP FreeBSD kernels on a VMWare virtual machine. This gives many problems, illustrated with this snippet from dmesg:

FreeBSD 6.2 sometimes stops booting the kernel, with the last message on screen:

This was a SMP kernel. As soon as I switched back to a GENERIC kernel, I haven't seen this behavior anymore.

Something to investigate better whenever I have more time, but it's a good temporary fix

Update 28 March 2008: