I wouldn't consider not taking my e-ink reader to the pool/beach at Cancun. I think it's one of the primary advantages of them. I tend to chat with people around me and they keep an eye on it if I have to leave it unattended for a couple minutes. If I play water volleyball or something I take it with me and leave it on a table where I can keep an eye on it. I'm willing to risk the $150 replacement cost for the benefits. I've been doing it for 4 years without a problem.
I have an Aquapac that I use when I'm in the water and it works great. Water loungers, pool floats, swim up bar or hot tubs. If you get a rain shower you can keep reading while people with paper books scramble for cover. I'm not interested in the new touch screen models because I don't think they'd work well in the Aquapac.
http://www.modernoutpost.com/gear/de...aq_360_pda.php
I used to take a paper book with me on the trip because I was worried I might break the ereader but now I just download 20 books on my iphone as a backup. I've been fortunate though and never broke an e-ink screen.