I'll believe it when I see it.
From the betas I've seen so far, it's just more eye-candy, and not stable.
Lots of vulnerabilities have already been found in it - I just hope they get fixed before release!
They've always touted the next release as being more secure than previous - Esp. with 2k and XP, but it's always turned out to be BS?
Heck, my Win98 partition required less effort to secure than my 2k partition, and was never vulnerable to stupid worms like Blaster and Sasser.
Now, as these are betas, I'm reserving judgement, but to put things in perspective, I was running the Opera9alpha2 (And now beta1) and it was STILL more stable and faster than both Firefox and Internet Explorer...
If Vista was showing that kind of stability in beta I'd be a lot more hopeful, but it isn't.
Worse yet, testing in the office has shown that several apps, both retail and custom, have 'unexpected behaviour', which means re-tooling them and/or waiting for new versions...