Today I coded a 'Save all' debug logs functionality for empathy ( Bug 592994 )
Yea, 'twas a handsome amount of code for anyone's second fix :) , but choosing this was a conscious decision! While looking for a resolution, I was exposed to some of the important and frequently used data structures in GTK, like GtkTreeModel interface and its GtkListStore and GtkTreeStore implementations. I used widgets like GtkComboBox, GTkToolBar, GtkToolButton and Gtk core reference - stock items while creating a custom button as this.
This bug was a must for me!