Equally, accepting free notebooks from Microsoft is the wrong move for bloggers to take. Keep them and you have zero credibility without disclosing clear as day that the machine you are evaluating it on is worth a tidy $2,200 and Microsoft gave it to you free. Even then, I doubt you’ll have much credibility.
Send them back and request a site from which you can download Vista and test it out on your current system. Lets see if Microsoft has enough confidence in it’s own products to do just that.
The argument that this is just a product reviews program is garbage. Bloggers aren’t professional reviewers – our strength and value is that we aren’t. And if it was, the systems would have been delivered with the expectation that they would be returned.
No ethical journalist would ever take a free notebook from Microsoft. Neither should any ethical blogger.