After a quick source review I have a few comments:
- There is no way to set a value by key. You have get_active_key but not set_active_key.
- I think you should create method aliases that are more inline with PEAR naming conventions. It will help make the package eaiser to use for people who are used to working with PEAR packages.
- You don't do any type checking. I don't think PHP-GTK 2 will react nicely if I try to set a key to an object. It would be nice if you caught that problem and returned a PEAR_Error before PHP-GTK catches it an spits out a nasty error message or crashes.