Here's a cheery little article for you (US-CERT discloses security flaw in Intel chips
): apparently, using Intel CPUs in 64 bit mode, using virtualisation there is a potential exploit, due to differences in the way that AMD and Intel implement the x86-64 instruction set.
"Besides Microsoft and Intel, vendors whose products are affected include Joyent, Citrix, Oracle, Red Hat and SUSE Linux, US-CERT says."
Not at all potentially widespread, then. Ho, hum.