I’ve been using OS X in a VM under Windows using VirtualBox for some time now. While researching potential workarounds for some of its limitations (e.g. 1440x900 max resolution) I came across the VMsvga2 graphics driver for OS X under VMWare.
I tried this setup with VMWare Player 3.0, without VMsvga2, and was not impressed. However, VMWare Player 3.1.1 is much much better. With VMsvga2 it is a much better setup than VirtualBox. Better yet, rather than installing from scratch, which is a pain with VMware, I converted my VirtualBox image to a VMware one and then used the ISO and VMDK from here.
Not only is VMWare faster (at the moment) for OS X guests, with a couple of tweaks to the vmx file, it is also more stable. Here are the changes I made:
smc.present = "FALSE"
monitor.virtual_exec = "hardware"
monitor.virtual_mmu = "software"
guestOS = "darwin10"