From the Digital Library "About Us" page:
The Digital Bookmobile is a community outreach vehicle for public libraries to promote downloadable eBooks, audiobooks, music, and video. Developed inside a 74-foot, 18-wheel tractor-trailer, the nationally touring vehicle is a high-tech update of the traditional bookmobile that has served communities for decades.
The Digital Bookmobile creates an engaging download experience around the host library's digital media collection and 'Virtual Branch' download website. The vehicle is equipped with broadband Internet-connected PCs, high-definition monitors, premium sound systems, and a variety of portable media players. Interactive computer stations give visitors an opportunity to search the digital media collection, use supported mobile devices, and sample eBooks, audiobooks, music, and video from the library.
The Digital Bookmobile is hosted by individual public libraries in support of their download services and is operated by OverDrive, Inc. To see if your public library offers download books and more, visit the Digital Media Locator.
Bookmobile schedule as of 8/4/2008 lists stops through August 13.
A birds'-eye view of the bookmobile is available on Flickr.