The iPad is a great device. Some say magical. But for all its convenience, apps and ease of use, Apple's tablet and others like it are still mostly just expensive toys. With a focus on gorgeous displays and a size and weight that make them easy to curl up with, the obvious appeal for these devices is consuming media like movies, the Web and eBooks. But it wasn't fun and games that made the PC such a dominant force in modern life-- it was work.  Americans are work-obsessed, and when it comes to getting down to business with spreadsheets, word processors, Photoshop and the like, 9 times out of 10 a sturdy laptop or desktop still trumps a sexy tablet. For tablets to replace PCs, they have to go beyond the sofa and the bedside table-- they need to enter the home office, too.