I heard about Hyper-V supporting CIFS as VM storage as well, seems like everybody is going that way.
You can PXE boot your ESX severs (and most Linux/Unix servers out there) from NFS too, i have done this several times with CentOS and it works great, I have yet to try this with VMWare, but it is supported AFIK.
There's a blog from a guy named Chris Wolf about PXE booting ESXi servers, it is old, but the procedure hasn't change much since it was written: http://www.chriswolf.com/?p=18
The procedure is similar on all Linux flavors.