My primary point is that the tablet is fully intended to handle mobility computing, not the heavy number-crunching of pro-grade software. Spreadsheets can be displayed and modified easily on such a device but just as everyone else has said, I wouldn't use one to create a spreadsheet from scratch unless it were a very simple one.
The same essentially holds true for word processing, photography, image editing, etc. It lets you look; it lets you make minor changes (somewhat gross changes in the case of image editing) and simply gives you the ability to have all your files pretty much at hand wherever you go and do almost anything with them even when you're away from your desk. It also doesn't take up near as much tabletop area as a laptop because, well, you don't have to put it on the tabletop in the first place.