nomis5 - 8:40 pm on Dec 4, 2011 (gmt 0)
Make sure you choose the version which will be suported by Google and Bing the most. It is a real pain in the neck to implement Rich Snippets, you don't want to do it all again in five years time.
Another downside, according to scrapers, is that labelling up your pages with Rich Snippetrs enables scrapers to steal content more easily. Again this can be mitigated by only supplying the information YOU deem worthy of being classified by Rich Snippets.