The ACES stuff is the partial implementation Walter McGinnis and I did for SloanSpace last summer. It works OK for them but isn't complete, and abuses the iCalendar standard in ways that Outlook allows but other iCalendar clients don't care for. This was meant to be nothing more than a short-term solution since Sloan had already committed to funding dotLRN.
Doing a complete job requires that the calendar package become timezone-aware. Neither the 4.x Calendar and ACES Calendar packages are timezone-aware and the lack of this information is what led to the rather ugly Outlook-dependent hacks on the iCalendar output mentioned above.
I'm not sure where dotLRN is on this ... slipping in a hack similar to what I did for SloanSpace would be easy, adding full support easy once timezone-awareness is implemented in the calendar package would be easy, but impossible before.
