[whpalmer4]

Both the iPhone and the Mac have to do a sync for the change to get to the Mac, and the iPhone has to do the sync first. They don't communicate directly with each other, but with the central server. Syncs happen on demand (when you tap the sync button), a minute after you make a change, an hour after the last sync, or when you quit the Mac app. So, if you make a change on the iPhone and it syncs the change to the server, it might be as much as an hour before the Mac picks up the change by itself, and of course longer if you didn't leave the application running, as it only syncs while it is running.

Another possibility is that the iPhone app didn't run long enough after you made the change to get a chance to sync.

Think of it as communication via putting notes on a bulletin board. You put the note up when you make a change, and when you are there, you look to see if there are any new notes for you. Otherwise, you only look at the bulletin board occasionally, and a note for you might sit there for a while before you see it.