I have noticed as I transfer photos to the iPad either via Photo Stream, through iTunes or even the Camera Connection Kit itself the photos will be compressed and loose noticeable quality.
It actually looks like JPEG compression on the photos but I am using PNGs which should have no loss. Even JPEG at 1% compression look like around 20% compression.
EDIT:
I just verified.
Source Photo = 2.22 MB
iPad Actual Size = 1.6 MB
Source Photo = 4.67 MB
iPad Actual Size = 1.0 MB
It actually looks like JPEG compression on the photos but I am using PNGs which should have no loss. Even JPEG at 1% compression look like around 20% compression.
EDIT:
I just verified.
Source Photo = 2.22 MB
iPad Actual Size = 1.6 MB
Source Photo = 4.67 MB
iPad Actual Size = 1.0 MB