It seems to me that availability and interest in ebook readers has catapulted recently. Much of this surely is related to the success of the iPhone (and presumably other full-screen mobile phones) and Amazon's Kindle. I have off and on for years used a Palm device as a reader, converting my own text files, html's, and pdf's into suitable e-texts. I would do things like export articles from the Anchor Bible Dictionary out of Accordance and put it into the device for portable and especially late nite reading. But now with an iPhone, the screen has improved, and with Stanza for the iPhone and Amazon's Kindle iPhone app, things have gotten even better.
However, one of the great advantages to the days when I used a Palm device is that I could roll my own e-texts. The ability to pull content from where I could get it offered the greatest advantage. If you have an iPhone or a Kindle and need an e-text management tool, there is an app called Calibre that may be for you. Calibre allows you to roll your own texts for use on an iPhone or a Kindle (and it does much more as well).
Amazon's entry into the field means that some ebooks of interest will be available to ministers and bible scholars, but still, relatively little for now. I suspect it will long be the case that the most useful e-texts we will load on our own devices will be pdf's we've pulled off our library full-text databases, and other custom sources, and that most often the capability to put our own content onto these devices will provide the greatest utility.