http://www.vmware.com/files/pdf/VMwa...ualization.pdf

"Due to high hypervisor to guest transition overhead and a rigid
programming model, VMware’s
binary translation approach currently outperforms first generation
hardware assist
implementations in most circumstances. The rigid programming model in
the first generation
implementation leaves little room for software flexibility in managing
either the frequency or the
cost of hypervisor to guest transitions

Because of this, VMware only takes advantage of these .
first generation hardware features in limited cases such as for 64-bit
guest support on Intel
processors."