In the calendar reminder settings, these are the two options: "alert" and "status bar notification." However, I'm a little confused between the exact difference between the two. Is alert simply the same thing as status bar notification except that it will play a ringtone if one has been selected? But if that's the case, why is there a ringtone option even when you have chosen "status bar notification?"
"Alert" will cause a new window with the event details (or a list of events with their info, if more than one) to pop up on top of the active one and take focus when the reminder occurs. It also puts a notification icon in your status bar tray. The "status bar notification" setting causes the status bar icon to appear but doesn't automatically bring up the details dialog.