A new release of CSS3 Pie has been announced, PIE 2.0 Beta 1. It comes with lots of goodies such as a bit of background size support and rgba support in simple linear gradients and box-shadow rendering. For a more precise break down check out the release post, as not all of the newly supported features work in all contexts.
I had written a method for integrating version 1 of PIE into WordPress for plugin and theme authors but as the new version of PIE uses a different load method, I found it useful to post an updated method. The main difference with PIE 2.0 is that the htc file is very small now (