Rasputin - 3:29 pm on Apr 9, 2012 (gmt 0)
Netmeg, I don't know what doesn't make sense but I'm pretty sure microdata doesn't exist to get one over on google but rather to help them to improve their SERPS - but that doesn't work if the results aren't policed in any way, it just becomes another grey hat SEO technique.
Real world example: yesterday I was looking at a profitable search result and noticed the first result had 5* showing and a 'review' - but I knew the site was just an iframe and a menu supported by a lot of link exchanges so I was surprised that they had the stars showing or that anyone would submit a genuine review to an affiliate iframe site.
It was clear when I looked at it that the rating was fictitious and added just to get the stars in google serps. Which had worked, so well done to them I suppose. But it means everyone else on the page will now do the same thing.
If a poor site with reviews ranks higher than a good site without reviews, or at least stands out better in the serps because of the stars, then it becomes yet another 'do it to please google' task rather than a 'just carry on doing what's best for my site visitors' task (like splitting stuff off to subdomains without altering it or adding needless text to photo gallery pages so they don't get a site hit by panda etc etc)
Incidentally for certain things I think stars are an excellent idea - hotels where reviews are submitted after people have stayed etc, but think they should only show in the serps for sites like these where the ratings are verifiable, the sites are reputable and the rankings very likely to be genuine.