I did a rebuild of my database, and things like iCal Syncing and what not started working and things are much snappier as well. (I didn't test for all known issues w/ iCal, but at least it doesn't take 10 minutes to load iCal Sync Preferences pane in OF.
As far as i unterstood Omnis sticky iCal post in this forum OF is unable to sync with non-local calendars and ical displays the mail calendar in a separate group. OF does not display my .Mac Mail calendar in the sync config dialogue. :-(
I'd be happy to hear about anyone who is able to do this syncing!