Over the years Apple has made the iPhone and its iTunes software do more in the way of syncing files, applications, and other settings. As a result, it's arguably become a more complicated process than it was just a few years ago, which is why iOS 5's iTunes-free and iCloud-powered features are a big deal.
According to a report by former Macworld writer David Chartier on his personal blog, a data point to back that up is that "about 50 percent" of people coming into Apple's retail store Genius Bars for a fix are coming in with iPhones that have never been synced with a computer. That's besides the computer used to set it up in the first place, a service Apple offers in its retail stores free of charge.
That means those users don't have any new software updates short of what their device was on when being unboxed, and if they don't have a MobileMe account--or a tie-in with some other Web sync service--their contacts, bookmarks, and calendars reside only on that device.
The sourcing on that metric is an anonymous "little birdie," so perhaps take it with a grain of salt.
When Apple launches iCloud in full alongside iOS 5 later this year, the software and cloud service combination promises to let users sync their device with Apple's cloud, making an automatic back-up of just about everything. This goes hand in hand with a new on-device restore feature, which can sync up a device you just took out of the box to match the precise contents of one that might have just been run over by a truck, or put in the blender by the "Will it Blend" guy. That should make it a bit easier for Apple's support staff, and even the users who may regularly back up their iOS devices, but perhaps didn't get a sync in ahead of when something went wrong.