it's been a while since I last used Ubuntu and it looks like that Ubuntu changed a lot. Some fast questions would be is current default (Ubuntu 11.10) panel still gnome-panel or is it unity-panel or so? I know that it is possible to integrate into messaging panel, although my program is not oriented towards messaging (imo neither is ubuntu one), it's a google task synchronizer. What is the way to add my program to clock panel? A subquestion (a little abstract, but don't know how to address) would be, how is the calendar applet made and what are the requirements to make such?
Very good question. As I understand it, libido is responsible for the non-menuitem items in the indicator menus. I mean the calendar, media controls, etc. If I understand correctly, you should be able to add menu items as usual, like the "Time & Date Settings..." item.