Parallels (best know for enabling virtual PCs to run on Macs) now offers a product that allows you to run any PC or Mac app (including PowerPoint and Keynote) on an iPad: Parallels Access.
How does it work? You need to install software on your PC or Mac that beams your application screen to your iPad. But Parallels Access is more than a simple remote access tool: adjustments have been made to add iPad-specific controls to PC or Mac apps (copy/paste, scrolling, etc.).
The service costs $80 per year, per machine you want to broadcast.
My take? I still think that the current iPad user interface is not suitable for intensive office work: you start missing a keyboard and a big screen when working for 8 to 10 hours per day. So I do not expect people to use this app when they are 5 meters away from their desk machine. Instead, it provides convenient access to crucial office applications when away from your desk (last minute changes in the taxi on the way to the sales pitch for example).
The pricing is also clearly aimed at the large corporate market. If you are interested in this type of solution, it might be worth to check out Splashtop.