This past year my partner and I have bought several mobile devices. We are using them for business and learning to manage and secure them. But the Droids, Droid tablets, Iphones, and Ipads are not computers. There is still a LOT they cannot do. Some businesses can and do use devices now, depending on their needs. But Apps are not Software programs, and unless you want to pay monthly fees for online versions of software you use (Quickbooks coming first to my mind), or setup your own server for remote access (we are back to using a computer here), you mainly can use the devices for your communication needs. There are some apps out that help you do file management and networking, but in my experience they have a long way to go for ease of use.
Still, I am constantly amazed at all the things I can do with these devices, and all the apps coming out.
I am sure these next few years will blur the line between devices and computers, but as for now the PC is still alive and well!