We are in the process of implementing Google Rich Snippets into a customers web site. Specifically to provide ratings to travel vendors and travel destinations, which will appear in search results on Google as google snippets. These will be delivered in Cake PHP. Also we are considering using it for some product ratings for e-commerce sites delivered in Ruby on Rails. We may even consider adding it to WordPress sites as a way of rating the content described on the page.
Of course the immediate concern was which technology to use microformats or RDFa? Not that it should be a big concern but we have to support whichever technology we implement.
Searching microformats vs RDFa on, brought up a ton of articles, and in depth debates on the subject.
I think Googles approach is a good one, they support both of them so we can use whichever standard we prefer.
As a development company we inherit a lot of work started by other development companies, so we will also support both. If we are creating or adding them from scratch to a site however, we will choose RDFa.
Initially I thought the opposite because microformats seemed more intuitive and easier to implement. After more research however, it seemed that RDFa would win out in the long run, and be more flexible. No one can know for sure though and I guess the best solution for everyone would be for them to just merge as a standard.
For more detail on the subject Evan Prodomou has a good write up RDFa_vs_microformats