"With CS4, Adobe added XML import capabilities in Premiere Pro. In CS5 they have now also added XML export, making basic round tripping possible between Final Cut Pro and Premiere Pro [and Avid]. In this tutorial I give an overview of how to exchange projects between Adobe Premiere Pro and Apple Final Cut Pro. ... But the supported options for motion graphics are very limited."
Exact information on supported effects, transitions, composite modes, etc. for FCP exchange can be found in Premiere Pro Help. Also, feature overviews on open workflows with Final Cut and Avid software are on the main product page (Avid exchange is with AAF sequences + OMF export). Here's Joost:
Update: in a Comment below the fold, Joost also found that XML from Premiere Pro CS5 imported into Final Cut Express 4.