If you sync seamlessly across devices, people will love you for it. It’s why I love the Apple ecosystem. I add a calendar event to my desktop, iPhone, or web app, and it automagically appears on the others. All of my mail is synced in all of these places so I never have to worry about missing email or knowing whether I replied or having to delete the same messages over again. The amount of time that this saves is invisible, yet invaluable.
It’s also why with all the different Twitter apps out there, Echofon is my preferred client. It syncs where you left off in your Twitter stream. When leaving the desktop, it’s possible to pick-up at the same point on the iPhone and vice-versa. Others will implement this soon.