SmarterTools,
First of all, your calendaring program is pretty awesome.
That being said, if you want to get serious about users really dedicating themselves to your calendar in SmarterMail, then you MUST start allowing them to create a calendar with a CalDav feed.
All of our organizational websites use a master calendar and I have coded CalDav support. Only users who use Gmail, Outlook, and other calendar programs can "subscribe" to it.
From what I see, you guys do a great job of events going out. But SmarterMail lacks events coming in. Please consider.
Thanks,
Ron