My local public library allows you to take out electronic books now, using both OverDrive and NetLibrary. I've downloaded both onto my laptop and this weekend started my first ebook using Adobe Digital Reader. My thoughts:
At first it looks like you only have two choices for font size, but multiple clicks on each tab will increase and decrease several times, so you can make as big or small (even to having both pages on a small screen) as you like. A plus.
The page numbers of the original, in this case a mass market paperback, are included on each page, regardless of how large your font is. Big plus! Book groups can reference a particular passage by page, not by chapter. I don't see why this is a problem, but it's the one downside to the Kindle (I anticipate Amazon fixing that very fast). Also, another big plus is a running page tally on top (75 out of 204, for example). I like to know how far into a book I am. Again, the Kindle doesn't do this within the text (it does provide a graphic on the front menu page, but not actual page numbers), but I think that will be an easy app someone will design this year.
Chapter headings are hyperlinked so you can jump to a chapter from a window that lists all of them if you are reading multiple books at the same time, or want to go back to a particular chapter. I can't figure out how to collapse the window with chapter listings on the left side of the screen so that text is maximized, but that's okay. Otherwise, like the Kindle, it will automatically open to where you ended if you don't close the book. I haven't used the bookmark option yet so can't tell you how well it works.
I'm reading on a laptop. If you're not using an ebook reader that can operate with OverDrive, reading is not comfortable. I tried to prop the laptop on my lap and get comfortable, but it's not easy with a regular-sized laptop (and a small cat who insists on sitting on your lap when you read). Would be even worse on a desktop. Big minus. Selecting an ereader that has an OverDrive app is one option, but I'm not happy with that selection for various reasons. Also, you use the arrows to turn pages (right and down arrows advance, left and up arrows go back). Don't accidentally hit the return button--it closes the program and goes to the Internet to the Adobe Digital Editions home page. Ask me how I know. I reflexively hit return about 5 times during the first hour of reading.
My eyes did get slightly tired as I tend not to blink when reading or working on a monitor, something I don't notice not doing with a regular book. The eInk technology might therefore make a big difference if you're an avid reader.
Big plus--being able to get online, peruse the library offerings, and receive it without having to drive to the library. Great option for home bound or people on a gas budget. Minor minus--it took 4 days for the ebook to be available to me, so somehow there is a limited number of digital editions that can be checked out.