She talks specifically about how she's using them in her CC Desktop framework to make tooltip creation simple:

CC_Tooltips extends the base GtkTooltips class to enhance the functionality. It handles a few "special cases" and forces the object to be a singleton.

There's a few bits of added functionality that are enhancements off of the standard standard tooltips PHP-GTK offers as well. Check out the full entry for more info on this and other features of the CC Desktop - including a code sample.