Think about the iPad this way: would a college student who needs to download a file from a school's web server and write an essay in Pages while looking up two PDFs really enjoy an iPad? I don't think so. Would a chef who wants to compare orders for her kitchen open 5 windows in Preview for OS X or jump back and forth between files on a third-party app for iPad? She'd just sit down at an iMac and use Preview. But would an iPad make sense for some tasks in those two use cases? Would the portability of an iPad be welcome in the student's backpack or the chef's countertop? Absolutely.
Federico from MacStories shares his personal story and how he manages to use the iPad as his main work machine. I find myself trying to use the iPad more every now and then and it works for me in a pretty limited scope. To see how it can be used if you really want to is pretty impressive.