Last week I blogged about jumbo frames being unsupported in ESX 4i.
Yesterday Charu Chaubal, Sr. Technical Marketing Architect at VMware blogged the following;

I am happy to say that this is merely an error in the documentation. In fact, ESXi 4.0 DOES support Jumbo Frames on VMkernel networking interfaces. The correction will hopefully appear in a new release of the documentation, but in the meantime, go ahead and configure Jumbo frames for your ESXi 4.0 hosts.

http://blogs.vmware.com/esxi/2009/12/esxi-40-supports-jumbo-frames.html
Although Jumbo frames being unsupported might not be an adopion blocker, this is quite good news for companies willing to use ESX 4i.