O.K., now I've done some research, so I'll answer my own questions.

First, Mobile Read is an outstanding web site for anyone new to Ereaders. It has a well-developed forum that should answer anyone's questions about these cool toys.

Second, there are several Ereaders on the market besides the Sony and the Amazon Kindle. The Kindle has a user-replaceable battery (as do many other brands) but the Sony does not. They all get from 6500 to 9000 "page-turns" per battery charge. No power is being used when reading, just for turning the page. However, when listening to music on these devices the battery life is much shorter. The Kindle has had some issues with battery life expectancy; some users report the battery refusing to recharge after as few as two months.

All the units have internal memory and also support memory expansion (either SD card or USB flash drive or both). You can store up to 1500 books on a 2 GB SD card! Most of the units weigh from about six ounces to about twelve ounces. The Kindle is unique in that it features a QWERTY keyboard that allows you to add notes, much as you would write in the margins of a paper book. It also features a built-in dictionary (not sure how important that is -- you can just download a dictionary into any of these toys).

Anyways, I'm going to do some more research, but I'm gonna' get one of these. My days of lugging four pounds of books on multi-day trips will soon be over.