I have both a tablet (iPad) and a Kindle 3G.
There are advantages and disadvantages of both:
Kindle:
For: Lighter and easier to hold. Easier on the eyes, especially for a marathon reading session. You can place your hand on the button and instinctively flip a page as opposed to moving your hand and turning the page on the iPad (iPad is closer to a book experience).
Against: Can't read in a dark room, so if its lights out then you can't read in bed.
iPad:
For: Backlit display, can read in a dark room.
Against: Heavy ... and feels heavier after a while. I must say I haven't been able to read for a long time on an iPad, and the eye strain is a small factor, but mostly that it has so many other things that you can do with it (I'm easily distracted).
I purchased the Kindle mostly for the kids, because I can leave it with them in their room and know they can do nothing else but read. If the iPad is in the room, then sure enough little reading will get done. I find the same seems to apply to me!
