The announcement of vSphere 4.1 is officially set for next week, July 13, virtualization.info has learned.
We cannot confirm yet if the product will be actually shipped that day or just announced.

virtualization.info already published the list of features that will be shipped with this new major release, as well as a VMware report about the performance improvements of many components.

An additional interesting detail is how VMware has enriched the offering for the SMBs. 
The new Essentials Plus edition in fact will include more features:

VMware vSphere Essentials Plus—This kit includes all the features of vSphere Essentials, plus High Availability and Data Recovery to automatically recover your data and restart your virtual machines in the event of system failures; with vMotion technology, now you can completely eliminate planned downtime during server maintenance.

http://virtualization.info/en/news/2010/07/vmware-will-ship-vsphere-4-1-on-july-13.html