This might seem obvious to most, but the pen itself and the ability to ink over an image is incredibly useful.
Yesterday, I received a form in a PDF document that I needed to print, fill out, scan and email it back to the person that sent it to me.
With the tablet I just printed it to a tiff, opened up the tiff and filled it out by just writing on the image using the pen and then just emailed back the resulting document.
So simple and no hassle.
Faxes (remember those?) are just as easy as our corporate email system is tied into a fax system: the fax arrives and gets emailed to me. I then ink all over it and fax it back via email.