My wife's job at the office will never be converted to ipad as she has to do multiple complex spreadsheet displays simultaneously. She has twin screen workstation and wishes she had 4 screens. In the field, however, she has a company laptop with one of those security dongles with the rotating key. (Required by Federal Banking regulations) but if that security issue could be eliminated, I'm sure her field needs could easily be met by an ipad. ipads already have presentation apps and a way to connect to a conference room or theater video projector. Some of her counterparts are already using ipads in this capacity. I have one of the ipad to VGA connector adapters here and it is actually easier to use than the laptop switch to external VGA. So, if necessary, ipad to larger screen area is not impossible, just not that well known. There is also an hdmi video and audio export adapter than can be used if the presentation has the hdmi input and requires audio.
The real limitation for the ipad right now is the applications for spreadsheets. I've looked at all of them in the app store and they all suck. What we really need is for Microsoft to create a powerful office set to run on the ipad for word, excel and powerpoint. That would be a big accomplishment.