Invaluable! Rated 5 out of 5 stars

Update + Reply March 26, 2012: Got it! Just goes to show how long I've been using Lightning without bothering to check on new button possibilities. Thanks for the tip! Welcome to the 5-Star Club!
Nearly almost perfect.
The only thing missing for me is a button for appointment searching - a feature which is only available via menu (i.e. not defined as a shortcut).

This review is for a previous version of the add-on (1.5.2). 

You can add such a button since Lightning 1.3 to the calendar-specific toolbar.