Well, I don't know about those of you who state that it's readable with polarizing sunglasses on. I always use polarizing glasses and regardless, I'm still not able to read easily. Better than with no sunglasses but not really good.
The best thing I came up with was changing the screen so that the background is black and the print then, of course, white. I usually use a small print but with the black and white I found a bit larger font works better for me.
In reply to the " just don't use it in the sun", I just have to comment that many of us like to sit in the sun and also read at the same time. Being able to use the ipad for that purpose would be great