Adult learners who need to develop basic skills can participate in activities within their zone of proximal development to build their sense of self efficacy, and have experiences of mastery with concepts or skills that might at first seem untenable. I'd say that V's theory is really central to work in adult literacy, at least for me. I like to use shorter more difficult readings to push students' ability to interpret a text in small doses, or present a multi-step math activity that asks them to perform calculations, but also draw conclusions from their results. I'll post some samples of this type of work if you want to check them out.
In Bridge class planning, we do a lot of research to find materials that provide opportunities for students to engage with texts, data and visuals that might be slightly outside students' usual discourse, but that connects to their career or post secondary plans. Even so, I think the ZPD is the place to reach after some preliminary generating prior knowledge and "buy in" activities that promote a spirit of inquiry around a guided line of questioning.
The zone of proximal development can definitely exist in these virtual spaces---transferring successful activities that might have been completed on paper to a shared public space online is one way to challenge students' boundaries around academic engagement and introduce a larger context for coursework. I guess I am interested in finding ways to use Web 2.0 push the limits of students' analytical toolbox, and provide new opportunities for them to demonstrate or re-present their skill sets.
Also, have you heard about Webb's depth of knowledge chart?
This builds off of Bloom and Dewey's work to present levels of "Cognitive Rigor" that can help guide instructional design and lesson planning. I first encountered this model when the GED testing service announced they were going to use Webb's model to guide the design of a new test. Here's a link that explains more about Webb.