The mainstream technical press has been working on its Windows Vista Beta 1 stories for a while, and their coverage went live today. Here are some samples:
eWeek: Beta Testers Get First Look at Windows Vista
PC Magazine: Hands On with Windows Vista Beta 1
CNET News.com: A Windows into Vista (interview with Jim Allchin)
Information Week: Windows Vista Beta Arrives
Ed Bott 
Win XP hidden feature blocks virtually all malware and spyware
Here is a summary:
Link
I believe it is fair to say that Microsoft INTENSELY does not want word on this to get out.
Are you kidding? This is not a “hidden feature.” And you can read all about it on a number of Microsoft Web sites. In fact, the article you pointed to drew all its information from Microsoft TechNet.
The problem with LUA in Windows XP is that the OS and existing programs aren’t set up to support it. It becomes a support nightmare. Windows Vista has been architected from the ground up to support LUA.
In fact, Carl Siechert and I spend many pages in the upcoming update of Windows Security Inside Out talking about LUA’s pros and cons.
But hidden? Deliberately? Not at all.