Be aware that the initial release of Ubuntu Karmic contains a bug that affects PHP and PEAR, whose fix came a tad too late to make the initial release. The bug is fixed, and will be included in upcoming updates from Ubuntu.
From PEAR’s perspective, the key issue relates to the zlib library. This is evident in any attempt to install or upgrade a package, since doing so involves downloading a tarball file that must be uncompressed. The bug causes some zlib functions to be unavailable to PHP, and the Archive_Tar code will silently fail due to this.
If you attempt to install or upgrade a package, it may appear to finish without error, but without a final “install ok” or “upgrade ok” message. This means the process failed. The workaround is to include the -Z argument, so that a .tar file will be downloaded rather than a .tgz file:
pear install -Z phpdocumentor