I've been downloading audiobooks from my local library for quite awhile now. And now, I've just finished reading my first Adobe Digital Edition on my Sony. I'm so glad we have this available to us now!! Jplumey's right, the PDF reflow makes it a little funky--strange page breaks, etc--but it's free, so I'm not complaining.
Charlieperry--it depends on the library. They usually require you have a library card before they'll let you download books. I live in California, and from what I can tell, I can get a library card for almost any library in California--some places are more restrictive.