For those unaware, VMware Workstation 6 has been exhibiting some significant stability issues under some 2.6.19 and 2.6.20 kernels. VMware Workstation would run and behave normally for some period of time, then crash with a VMM (VM Monitor) error, and take down the X11 subsystem, requiring a reboot of the whole system. I saw clear evidence of this under Fedora Core 6 x86_64 on these kernels, but not on the 2.6.18 kernel. There were several threads dedicated to this problem on VMTN, and a few possible fixes offered, but none worked. I resigned myself to running the VMware Server Console on my workstation, and housing my VMs on a different VMware Server system, which definitely has some benefits over running them locally, but I was bothered by this mysterious issue. My main workstation is a Sun Ultra 40 M2 with two dual-core Opteron 2220s and 8GB of RAM, so using that to drive VMware Workstation for my Windows needs is really the best option from a performance and functionality standpoint.
Since then, a FC6 kernel update to 2.6.22 was released, and rather than step back to 2.6.18 on that system, I tried going up to 2.6.22. That was about a week ago, and the VMware Workstation instance on my main workstation has been stable since. I haven't found any direct reason for the problem, or its resolution, but there you have it. Also, for those curious on getting the VMware Workstation components to compile and run on Fedora or other distributions, you'll likely need the VMware any-to-any patches found here.