The Microsoft CEO, Steve Ballmer, has admitted that Vista is "a work in progress", and that the company left too long a time period between the release of XP and the new OS.

Speaking at the Most Valuable Professional Global Summit in Seattle, Ballmer said: "Vista is a very important piece of work, and I think we did a lot of things right, and I think we have a lot of things we need to learn from".

"Certainly, you never want to let five years go between releases ... because it turns out many things become problematic when you have those long release cycles. The design point, what you should be targeting, we can never let that happen again. We had some things that we can't just set the dial back that I think people wish we could."

In the face of various consumer campaigns for Microsoft to keep XP alive, Baller said: "We have a lot of customers using Vista, and we have a lot of customers that are choosing to stay with Windows XP, and as long as those are both important options, we will be sensitive, and we will listen, and we will hear that".

Ballmer also joked about the ongoing $42 billion hostile bid process for Yahoo asking for a show of hands to find out how many in the crowd used Yahoo search, apparently after only a few hands raised he responded: "Wow, we offered 31 bucks a share".