Lots of reasons for .. main against seems cost... Our group is an avid IT users in games, and I have been using my Ipad for a few months now in my sessions as a player, and DM...
As well as the obvious gread pdf reader for books, modules, sources, stuff from DDI... its also good as a web broswer to look at compendium, and for use with Iplay4e to actually use your character at the table.
I have downloaded dice programs, and I use sync'd onenote to hold all my campaign notes, info, house rules and timelines....
As I have advanced I use splashtop to make my ipad a PC, (virtual session) and run mapping programs, Character Builder and Adventure tools as if I had my laptop with me, but with 12hours of battery life, instant on and a fraction of the weight.
When I play at the table, a program like Air Display makes my ipad an additional wireless screen to my laptop.. I can drag onto it my initiative tracker, or use it to hand out note, pictures, or maps....
So while it is expensive, I have found it invaluable as a tool, notepad, screen, reference and beats the laptop or huge bundle of books and papers I use to carry round..
Have taken some pics, if anyone is interested
