Looks good. The only complaints I have are coding standards related. The package itself looks interesting and is something I can see myself using at some point but never want to have to write myself ;)
I appreciate the documented examples on Google Code.
1. missing ?> at the end of files
2. some class members are not documented. Given the large source base and large amount of work it is to document everything I don't think this should prevent a vote but it should be fixed up before a stable release.
3. PEAR's member variable naming conventions are camelCase, not under_scores.
4. methods that return nothing should be documented as @return void, not @return.
5. try running the code through phpcs. It's not bulletproof but it usually turns up small edge-case PEAR coding style issues.