When asked the other day about what's missing from Windows Vista, Steve Ballmer refused to be drawn into the discussion. "I don't choose to go down that path, sorry," he replied. At today's official launch of Vista in New York, however, Ballmer opened up, rattling off a list of things customers can expect to see in Vista's successor.The revelation came at the end of a 90-minute unveiling of Windows Vista, Office 2007, and Exchange Server 2007. During the Q&A session that followed, AP technology writer Brian Bergstein asked Ballmer, "What's left to pursue in the next operating system?"

Plenty, it turns out. Ballmer pointed to "a bunch of work we still need to do" in tuning Windows to take full advantage of multicore microprocessors. For IT administrators, he said, there's work to be done making Windows easier to deploy and manage. And for developers, there's still WinFS to complete, the next-generation storage system that Microsoft dropped from Vista in order to hasten Vista's delivery. Ballmer talked of adding graphics and video support to the core OS. "From an end user perspective, there's so much more to do," he said.

And Microsoft needs to rejigger Windows for the world of software services. "There's a lot more service enablement you can expect to see from us," Ballmer said.

Not much detail, but it's a start. And it's a refreshing display of openness by Ballmer after clamming up a week earlier when I asked him to identify something that didn't make it into Vista. Understandably, Ballmer wants to keep the focus on what's here today, not what's missing.

But Microsoft better be prepared for more questions about what comes after Vista. Ballmer himself said there's "so much more to do." It's only natural that we want to know what it is.