Remember when the iPad came out and all the naysayers said "It's just a big iPod touch?" Well, my response was "Yeah, but wouldn't a big iPod touch be GREAT?!" It's like saying a 42" TV is just a big 13" TV. Yes, and sign me up for the big one! If I can have a larger screen, I'm all for it, and if I can have multiple screens, that's good too!
My colleague, Jim Karpen, wrote a preview of the $10 Air Display app from Avatron Software back in May and I've had a chance to play with the app, on my iPad and all I can say is "Holy Cow!"