I had the same issue on my MBP 2.3 GHz i7 quad-core 10GB 1600MHz DDR3 Running OSx Mountain Lion v.10.8.4. I changed the VM CPUs from 1 to 2 and bumped the RAM from 1GB to 2GB. I also changed the Optimization Performance from "faster virtual machine" to "faster Mac". I've been running this way for about 3 hours and my CPU usage has gone from 100% all the time down to about 8-12%. I still have spikes up to 100% when I open a new program, but I've been using Visual Studio for the last few hours and my machine is running better and staying cool. I'll update this if it changes, but is seems to be running well for now.