Okay, it sounds like 10 VMs per physical core is the agreed upon real world limit. I'll adopt that. Most of my VMs are LAMP servers (with 1 GB of memory) for various web and mobile apps I'm developing - they barely consume any processing power since no one is actively FTP'n/GIT'n/dev'n on them.
My current host is a SFF desktop with a Core 2 Duo E6600 2.4 GHz processor. But I just scored a tower with a XEON E5520 Quad Core 2.26 GHz proceesor, so this will replace my current host. Since it will be a host with the more powerful XEON processor, what would you guestimate as to how many VMs/vCPUs I may be able to get out of each core?