I've caught up on a few pending patches (one since 2005, erk) and packaged up a new Ruby PHP Serializer release.
This release fixes a few bugs, and adds support for serializing and unserializing PHP sessions. There's also a small test suite included, which passes on Ruby 1.8.6, 1.9.1 and JRuby 1.2.0.
Please let me know if you find it useful :)