I just got an email this morning from VMware inform that the official version of VMware vSphere 4.1 are available to be downloaded from the official website. There are a lot of improvement if you compare ESX 4.1 VS ESX 4.0.

Significant Improve on Scalability, IO control for both Network and Storage, Active Directory Integration on Host level, up to 8 vMotion concurrent session at 1 time.

For short review as what’s new on ESX 4.1, you can refer to the official link here.