Thanks whpalmer4!
Unfortunately, my reminder sync woes are not over. I think the problem originates in this:
http://support.apple.com/kb/HT3634
As explained in this document, calendars subscribed to on iCal are actually *pushed* to the cloud (and the iPhone) by MobileMe. So, as of iPhone OS 3.1, there is no need to manually and separately subscribe to the calendar on the iPhone. Actually, manually subscribing will result to duplicate OmniFocus calendars on the iPhone.
In practice, however, this works horribly: It takes hours, literally, for OmniFocus reminders to be pushed to the iPhone, and therefore I cannot trust that my system works.
The alternative is to use the "old" method (manual subscription), and tolerate the duplicate calendar. However, in that case, I risk receiving duplicate reminder alerts on the iPhone, which can be quite confusing.
Perhaps OmniGroup could jump in and update their sync instructions in light of the Apple Support Document above.
Any comments? Thank you very much.