This is how they describe Liquid Textbooks to academics (excerpt from their site):
By comparison, Symtext enables you to teach better courses by assembling best of breed digital content from multiple publishers into dynamic, continuously evolving "Liquid Textbooks", thus ensuring the highest possible quality content for students. Unlike traditional materials, Liquid Textbooks include not only traditional content like chapters, cases and articles, but podcasts, videos, presentations - curated Flickr feeds - data files, and many other types of digital files. (We'll clear the rights and do the work to make sure your students gain access to your Liquid Textbook through your School's Learning Management System.)
Web 2.0 approaches to digital content, such as this effort, may eclipse the focus on static digital textbooks (i.e. digital versions of hardcopy textbooks) sooner rather than later.
Digital initiatives, whether applications or hardware, are emerging and evolving at a increasingly quicker pace. Where it is going to end up, nobody knows at this point. But we can't wait until the dust settles. Campus stores need to quicken efforts to adapt to the digital future, and a changing role within that future.