Nothing gives me more professional satisfaction than seeing my work being used for practical applications.
One of my long-standing gripes with Views is the inability to alter the behaviour of existing Views handlers (e.g. fields, filters, etc.) without having to subclass the desired handlers to add new functionality. While the subclassing approach is fine when the functionality targets a new field type, it is not ideal if the change required should affect existing fields, across different types of handlers.
I was recently commissioned to create a module that displays tooltips on field headers, regardless of field type.