Skirting the political issues involved, he cites the move from CVS to SVN+Trac as a major factor in his decisiont to move.
The CVS repository has been migrated to Subversion, Trac is now used to provide repository browsing, issue tracking, and wiki functionality. The PHPUnit Pocket Guide website is now proudly served by lighttpd and the DocBook/XML sources of the book are now also publically available.
Whilst shocking and somewhat tear-sheding, I hope this move doesn't set a precedence for PEAR. Sebastians technical reasons for moving are certainly decisions I have made for projects outside of PEAR and I am happy to see another project make that jump.