It's totally relative to how you set the sync iirc. If you go to the screen size, probably not all that much more than what you see on the iphone/touch - Hmm perhaps it auto resizes - I thought you could set the sync size but it appears I was mistaken. Haven't ever really used that feature on the iphone but will be on the ipad!
well, one nice thing I have noticed is that the images are optimized for the iPad during the sync process.... This is HUGE for me as I shoot with a Canon 5D Mark II 21 megapixel camera and the files are really big. This should help cut down on the space needed to store my jpegs