I wonder how much these kinds of "mistakes" come from trying to create a paradigm where it looks like there is only one copy of something in a world where users

I wonder how much these kinds of "mistakes" come from trying to create a paradigm where it looks like there is only one copy of something in a world where users are already used to the fact that computers are copying machines by nature (your friends can not technically view your photos unless you upload them to flickr (provides flickr a copy), and the user downloads them from flickr (makes a copy to the user)). Similarly, you don't necessarily delete something off your iPod, you remove it from your iTunes library. The various players you have for music interface with your iTunes library, they conceptually don't read individual files (even though they technically do, that's how disconnected operation currently has to work). The syncing helps make things appear to have transparent access. You have one address book, the syncing between discreet devices happens in the background to support the illusion of a single instance. Time Machine is similar, in that there is a conceptual presentation that you're looking at the same file at different points in time, not that there are multiple files each containing different versions of the same conceptual content (even though it actually needs to copy a file to make a backup, even if it does some tricks by using hardlinks and is COW (I don't know the internals of TM)). Unfortunately, this goes against the majority of computer users' experience. While that's a good mapping to real-world physical devices, it doesn't work for things that are stored in distinct files. When I take a picture with my digital camera, it is stored on the camera. Now I copy it to my computer, and there are two instances. Now I upload it to flickr, and I still have the other two copies: I don't need to go to flickr to view the image. Vs address book entries, which are not usually stored in distinct files and have not traditionally been moved around and copied like files (UIs that do as an useful * extension* not withstanding), so the concept of keeping all data in sync is more natural to users.