Per the TrackBack changes in Movable Type 2.5, we've made the corresponding changes to the TrackBack specification:

• TrackBack pings should now be sent using HTTP POST instead of GET. The old behavior is deprecated, and support for GET will be removed in January 2003.


• In the RDF, the TrackBack Ping URL should now be stored in the trackback:ping element, rather than rdf:about.


• Changed the format of the sample TrackBack Ping URL to use the PATH_INFO instead of the query string.


• The embedded RDF used for auto-discovery no longer causes pages to fail validation.
  
• Added sample code for auto-discovery.

We have also released a new version of the Standalone TrackBack tool (documentation), which implements the changes in the spec.

Thanks to Paul Prescod and others for suggestions and guidance on making TrackBack more REST-like.