covers the state, pretty much.
Can check out ePub, Pdf, Kindle versions of books (Kindle only in the last year, epubs for the last three years, which is why I went nook on the ereader front to begin with), as well as lots and lots of audio books in either mp3 or wma format. Been using it for several years.
The eBooks are handled locally through Adobe Digital Editions and can be dragged to and from your eReader device (or, of course, read on the local computer). Similarly the audio books are handles through Overdrive and can be moved to and from the mp3 player with that. I don't do Apple, so I'm not sure if you use Overdrive or iTunes for an iPod.
Milwaukee County patrons can check out up to 10 items at a time and choose 7, 14, or 21 day check out time.
What happens is a custom DRM is placed on the file that expires after that time. The media remains on the eReader, but is not readable. You need to delete it yourself using one of the programs above, or just your local file system. Because the file is on your machine there is no way to "return early" when you're done--so if you use it a lot and push the 10 item limit, you want to choose the your checkout durations carefully.
Other libraries may vary, though.