I am running Windows 7 x64 both as a host and a guest VM using VMWare Workstation v9.

Here are the figures of Windows Experience Index for each instance, so you can estimate virtualization efficiency:

Host Windows 7:

Guest Windows 7 - VMWare Workstation v.9:

Guest VM is allocated 2 cores, out of 4 cores total on my Intel i7-4770.
As you probably have heard, Windows 7 uses logarithmic scale for its performance score.
On this scale, 0.6 means a factor of two, which exactly matches the above results for CPU performance.
It also means that there is no overhead here at all. Same as disk, btw, and almost no penalty in virtualizing memory.

Regarding improvement of Desktop Graphics performance, I found this article, which refers to Workstation v6.5:
GPU Virtualization on VMware’s Hosted I/O Architecture:

• […] test virtualization overhead while performing a GPU-intensive operation
• […] Also worth noting is the fact that VMware Fusion, on average, performed better than the host machine.