I finally found some time to write some documentation for the branch. I've created http://gcc.gnu.org/wiki/pph with some initial documentation on the pre-tokenization and pre-parsing work we are doing on the branch.
The big missing piece is a more detailed design document that Lawrence will be posting in the next few days. Lawrence, Ben, Jason, could you take a look and make sure things make sense? I've also updated svn.html with the location of the branch. Thanks. Diego.