I installed SEO Ultimate yesterday to get microformat support. It seems it generates a tag like that, when used as "Review":
<time itemprop="datePublished" datetime="2012-07-18" />
AFAIK this is only available with HTML5. So validating my webpage via w3c.org results in errors.
If I take a look at http://schema.org/Rating it shows an example without html5:
<meta itemprop="datePublished" content="2011-04-01">
As long as HTML5 isn't spread wide, maybe this can be used as an alternative?
It would be also nice, if the property "image" could be supported to add an image to a review.