As VMware hosts its first VMworld conference as a public company this week in San Francisco, its star is ascending.

Since going public at $29 a share Aug. 14, the company’s stock price has not closed below $51. Industry researchers note that 80% of the businesses using virtualization to improve utilization of their x86 servers choose VMware software. Some competitors hope to catch up to VMware, but their couple hundred customers each could fit into a phone booth compared with VMware’s 20,000. Meanwhile VMware continues to innovate, bringing virtualization to the desktop, embedding VMware directly into servers and taking other steps to maintain its lead.

But every company in its IPO prospectus has to acknowledge risk factors, and some of VMware’s could manifest themselves quickly. Virtualization player Citrix announced a $500 million acquisition of XenSource Aug. 15, while XenSource narrowly beat VMware to market Sept. 5 with plans to embed its hypervisor directly into servers, too.

Not to mention the Microsoft threat. Microsoft plans to ship its hypervisor, called Windows Server Virtualization, in the latter half of next year as an add-on to the Windows Server 2008 operating system, which is due out early next year. Although Microsoft has been slow to respond to VMware’s challenge with a competitive virtualization hypervisor of its own, when it finally does it will certainly be noticed by Microsoft’s sizable server customer base. Microsoft also argues that VMware’s popularity in server virtualization does not necessarily translate into popularity in desktops, application, storage and networking virtualization.

Still, as VMware hosts an estimated 10,000 attendees at VMworld 2007 in San Francisco, it enjoys frontrunner status. The venue is also the stage for other vendors in the VMware ecosystem to announce their own related products.

“[VMware is] clearly the market leader. There’s no question,” says Mark Bowker, an analyst at Enterprise Strategy Group. “They are gaining amazing traction in the environment.”

Virtualization software is designed to make a physical server act like multiple logical servers, improving server utilization by allowing IT managers to efficiently combine numerous computing resources on a single server.