Honestly, I have a feeling it is about as elusive as getting Google Sitelinks. My recommendation is to follow the Google guide for Rich Snippits and when the site gets enough PageRank and keywords hits, it will naturally start appearing.
Also be sure to watch your webmaster tools closely and address any issues Google finds. There is also a section called "Sidewiki" under the labs option to force the description text for the main site search result.
This page also has useful information and indicates your root cause why they might not be working:
Who is eligible for Rich Snippets?
Currently, review sites and social networking/people profile sites are eligible.
We plan to expand Rich Snippets to other types of content in the future.