New! BioPAX files are now validated using BioPax Validator v2.0 (errors were fixed). Available for download here (bulk download). From the next release ( scheduled to be released between 2 SEPT 2011 and 7 SEPT 2011) you will be able to also download BioPAX and other files formats from the pathway panel.
You can import the BioPAX files into external tools (e.g. Cytocape), integrate the pathways for network analysis and visualization. BioPAX files can be imported and integrated into databases.