The greatest disadvantages for me are:
1. Usability - very difficult to explain to average internet users how to administer the calendar.
2. (the bigger one for me personally) - Unable to delete single occurances of repeating events. My palm did this 8 years ago, I created a PHPNuke Calendar 6 years ago that did this, why can't I find a Joomla calendar that does?
If a group has an event every Wednesday, and it is cancelled on week, you cannot delete that week's event. You have to end the repeating event the week before, and start a new copy of the exact same event to start repeating again the week after.
For now, looks like I'm just switching to the embedded google calendar for Joomla.
Con: Never finishes backup, freezes every time. Really takes away from the usefulness of the com.
If you are experiencing problems - unlike most users out there - it's more appropriate to discuss them on the support forum, rather on a review site like this. After all, no software is without bugs and the only way to solve them is to get feedback from users like you.