Have you benchmarked your bare-metal vs. VM systems? I think you may be surprised how much performance you're losing. If you're not losing any performance I'd be interested as to your setup.
Also, the article discusses VPS systems which are generally much different than installing a VM on hardware you own.
I'll admit that the last time I tried to run an IO intensive task on a VM it was about a year and a half ago. (VMWare ESXi)
I think the processors installed in that box didn't support IO virtualization.
I've benchmarked filesystem with iozone tool and got more or less similar results for guest and host except "Pread" test where host is 20x times better then guest (my assumtion that this is a bug of virtualization software or misconfiguation from my side). I've performed test few times with same results.
My be I'm wrong but I don't understand where I could loose performance.
Why? You can run only one VM inside each hyprervisor. Or you can run only one IO intensive guest.
I hardly see any reasons to run my servers on hardvare instead of VMs in 2011.