Hello Vista, Goodbye Longhorn
David Coursey has an excellent piece on this announcement, with good background on the what Vista means in the market today. I disagree slightly with David though since I see Vista as an appropriate name for what they are doing with search and RSS subscriptions. As a higher vantage point enabling you to see the lay of the land, I get what they are after with the name. If they were to focus on the security aspects of the system, they would be lambasted by everyone - especially since there are still bound to be hiccups with security and patches along the way. If they tied the brand to such an issue, it would surely bite them in the ass eventually.
My thought is that it is merely intended to be different than Longhorn which carries too many negative connotations as it is due to the delays and constant scorn heaped on it by the open source and Linux communities. I bet they would have done it sooner, but were still unsure of the release date and did not want to have to change names twice prior to launch to ditch the tainted brand. The timing would seem perfect for them to start building up the hype and get most people's awareness away from the fact that Longhorn even existed. With the money they can put behind it, it should be a successfull plan.