I noticed my notes, calendar, reminders, etc were not syncing between my iPhone and iPad. I restarted both. At that point things would sync automatically from my iPhone to iPad, but changes on my iPad wouldn't sync to my iPhone unless I made a change on my iPhone as well. Using the iCloud.com web site, I determined changes made on the iPhone were being uploaded, but changes on the iPad were not.
I ended up fixing this by turning off iCloud notes on my iPad. It didn't ask me if I wanted to delete the notes, it just did. I then turned notes back on and somehow that fixed all the other iCloud services as well.