I started using Reminders.app as soon as I got iOS 5.0, and for me it mostly works very well. As soon as I got an iCloud account, of course I turned reminder syncing on there as well.
However I soon found that reminder syncing is still quite buggy at this stage. In particular, it doesn't seem to handle moving to-do items from list to list very well. I often got duplicate items and had other problems. (Note: This is not the topic of my question.)
So I finally decided to live without reminder syncing, and just use Reminders.app on my iPhone only. I turned off reminder syncing in iCloud. This did solve the problem with duplicate items, and I'm mostly happy with it.
But... I noticed that Reminders.app still seems to be accessing the network, even though I haven't configured reminders to sync with anything. (I am basing this observation on the little spinner in the status bar at the top of the iPhone screen.)
And whenever it does this, some of the old problems come back -- mostly sluggishness and jerky scrolling, etc.
I have verified that when I put the iPhone into airplane mode, the problem doesn't happen.
Does anyone know why Reminders.app would still try to access the network when iCloud syncing is turned off? What is it trying to do? Any way to turn it off completely?