The benefits of virtualization are quite obvious but when you start to really increase the density of virtual machines in order to maximize utilization suddenly it ain't such a simple proposition. The latest CPUs from AMD and Intel are more than up to the task of running 10-20 or more applications at a time. Most servers run out of memory and I/O bandwidth well before processing power. Recent announcements from the leading server vendors have been made to address the memory side by packing more DIMMs onto a single motherboard (including blade server boards), but you can only add so many Ethernet cards and Fibre Channel HBAs. Oh yeah, and then there's the switch ports to go with them (blade systems help a lot here).