Problem: When using the new Reminders app on OS X Mountain Lion, you can create and edit lists. However, the lists never sync with iCloud. In effect, the lists on your iPhone and iPad are never merged with your lists on Mac OS X.
Description: My conjecture is this is some sort of upgrade issue from Lion to Mountain Lion. If you have an e-mail account setup which supports "Calendars and Reminders" in settings, the Reminders app seems to attach itself to that account. So you can create and edit lists, but they don't sync. The interface looks like this with your list names different of course:
Solution: The fix is pretty straight forward.
- Go to Settings > iCloud
- Uncheck Calendars and Reminders. This deletes your current local list and calendars.
- Wait about a minute.
- Then recheck the box.
If you are in luck, you should see a set of lists for each type of account. So in my case one for my iCloud and one for my e-mail account. After this, everything should sync fine.
Note: The details were buried in this Apple Tech Note