This was an issue with Gnome 2 and evolution as well, but with the gnome-shell clock explicitly displaying a button for "Open Calendar" this has become a big usability issue for me. The problem is that setting up or accessing calendar events in evolution requires me to have some email subscription as well. So when I, as a "new" user, click on the "Open Calendar" button in the gnome-shell clock, instead of immediately finding a calendar application start up, I am forced to go through a wizard attempting to configure some email setup for me. Not only is it unintuitive, it completely discouraged me (and a few other users I know) from using what would have otherwise been a pretty useful calendar application with lovely integration into the gnome-shell.

It would be way more useful if evolution calendar could work irrespective of whether I have setup an email with evolution mail client or not.