I spoke with him on some of the things that had lead up to making this decision and he mentioned it as a two-fold reason: one was some personal conflict between other PEAR developers and himself and the other an issue of time and interest in the project. He still wants to see it succeed, but just doesn't see the time in his life right now to do his part. Pierre will continue to work with the PECL extensions and on the PHP internals groups to help improve and develope them towards future versions. Some of the extensions he lists as the ones currently in his development are things like GD, xmlwriter, Zip (of course), and filter.

It is just a normal process, things and people change. I would have preferred a slower switch, as I was working on my leave (giving lead for many of my packages to other friends).

Pierre's PEAR work can be seen on this page of his blog and includes all of his PEAR and PECL work as well as PHP internals and Pimp/Cairo/GD development work.

You can also check out the decision in his own words over on his blog.