I am not so sure. You are right about the beach, but honestly, how frequent is this case? Many people read at home most of the time. I myself actually own Kindle, and there is nothing fundamentally wrong with the device, but I am not still sure if I'll buy next generation if it wears down. The advantages of e-ink are still not that substantial, and I find myself read more often on iPhone or iPad. In the future, I find it more probable to own something like iPad mini or a very big smartphone, and not owning e-ink reader. For the rare occasion when I am on the beach, there is still printed stuff available.
To sum it up, IMHO the biggest problem with e-ink readers is that the advantage of e-ink don't outweigh the inconvenience to having another device. (unless the e-ink technology will substantially improve).