A Google Webmaster Help thread has one webmaster upset Google is not picking up his markup and showing rich snippets for his site in Google's search results.
Google's Zineb responded that Google doesn't show rich snippets for all sites, even if there are markup on the page. Back in December, Google reduced the rich snippets displayed in the search results significantly. So you shouldn't be surprised if rich snippets do not show for your site, in fact, you should be surprised if they do show.
To lay it on even worse, Zineb from Google told the webmaster they have "some quality issues on your site." Tisk tisk.
Someone needs to make an animated GIF of Matt Cutts saying "No Snippets For You!"
Forum discussion at Google Webmaster Help.