I use a computer to organize my recipes. I print them out since I don't have a portable one.
Even a small binder would work great. You could just stick your post-it notes on blank pieces of paper.
I still got one with cut out recipes glued on blank paper.
I think I would be worried about damaging an ereader while I'm cooking. If you do get one, make sure it has folder support. Otherwise it would be difficult to organize them.