We're pleased to announce that VMware vSphere 4 is now generally available. From the press release:

VMware vSphere 4 extends the previous generation VMware platform –
VMware Infrastructure 3 – along three dimensions: it delivers the efficiency and performance required to run business critical applications in large scale environments, it provides uncompromised control over application security and service levels, and it preserves customer choice of hardware, OS, application architecture and on-premise vs. off-premise application hosting.

VMware vSphere 4 enables transformative capital and operational
expenditure cost savings over and above what was previously achievable,
including 30 percent increase in consolidation ratios, 50 percent
storage savings, and 20 percent additional power savings.  With VMware
vSphere 4, even the most resource intensive business critical
applications will benefit from the built-in service level assurance
capabilities for availability, security and scalability. 

I think the vSphere product overview pages explains it well, but if you just want the bullets, this What's New in VMware vSphere 4.0 page sums it up.

For some serious reading, master virtualization encyclopedist Eric Siebert has assembled vSphere: The Missing Links – Every vSphere Link You Need to Get Started.

Greg Lato also has some screenshots of the licensing portal if you want to see our new very non-scary way to get your vSphere licenses: Quick Guide to vSphere LIcense Portal.

There's so so much more going on, like Converter 4.0.1 and vSphere SDKs and PowerCLI, but let's discuss those in the days ahead.

Let's close with Rick @ the VMware Knowledge Base Blog with these places to start and click through for his Top 10 vSphere KB articles: Let's Get This vSphere Party Started Right!