Still not convinced that virtualization is hot?

If VMware's barnburner of an IPO yesterday didn't sway you, then maybe today's news that Citrix bought XenSource for a cool $500 million should. And get this; XenSource only has 650 paying customers.

InternetNews gives us one reason why Citrix's checkbook flew open:

Citrix and XenSource officials on the morning conference call highlighted the huge potential for the XenSource products, specifically on Windows. XenSource has a working agreement with Microsoft that will ensure that Xen runs on top of Microsoft's upcoming Viridian virtualization hypervisor.

"We're building on top of the Microsoft Viridian base," Levine explained. "Think of Viridian as the proxy for the Xen hypervisor. When Viridan comes out, the same set of products that we've done will be on top of Viridian. The major differentiator will be that we can offer customers a choice, whether they want platform virtualization, a stack based on Xen or a solution based on Viridian."

So, it looks like someone didn't forget XenSource after all.