This was blogged in response to Robin Goodfellow's post on the Literacies site and I hope can also be read there. I agree with Andy that new technologies bring forward new ways of expressing academic ideas – and maybe we need to use terms like critical, reflexive, evidence-based, rhetorical etc to describe what is valued about academic ideas, and/or acknowledge that traditions of how ideas are valued and validated can change as in the oral-to-written PhD. I think it will be in discipline and micro-discipline communities that new practices emerge, become visible, and come to be valued, i.e. become part of a social practice and historical tradition. I do also agree with Robin, though, that use of the term 'affordance' is not always helpful – again my personal preference would be to focus on knowledge practice. Ong, I think, talks about writing as both a technology and a practice. In this vein, 'text' is also a slippery term - it is used to mean both specifically written or printed communications (communications using a particular technology), and communication of many kinds viewed through a particular analytical lens (hence 'multimedia text').
To get back to the practices, the 2007 British Library report into the information behaviour of school-age researchers has this on p.46: 'About 40% of UK schools found content in the learning directory by using a Search engine image search... Further about half of US (47%) and EU universities (47%) accessed the learning directory using a Search engine image search.' This is not young people in their personal, social practice but engaged in formal learning contexts. And actually if you have some idea what you are looking for, selecting from images (even images of text) can be faster and more accurate.
There is absolutely no doubt that academic practices are changing - in fact text and what we can do with it is probably changing faster than other modes are being adopted - for me the question is how we reframe in the new knowledge media landscape what is valuable about academic modes of communication.