I don't know anyone outside of geeks and friends/family that geeks have set up that have Bookmark sync, let alone people in large businesses where their desktops are run by the IS department.
I don't disagree. But as we move to a world with more virtualized environments and multiple devices, I think it will be more common. At the very least iCloud will make it standard in the iOS/OSX space. I can't help but believe MS will do the same for Win8.