From the book Designing Instruction for Technology Enhanced Learning (Patricia L. Rogers) there is a particular chapter by Lorna Uden (p161 onwards) that I've found really useful.
In the chapter (Designing Hypermedia Instruction) Uden considers some of the problems and concerns associated with using hypermedia. For someone that has always been an enthusiast for hypermedia this came as a genuinely new way of framing the problem.
Early in my teaching career I saw systems like Hypercard, !Genesis on the Acorn Archimedes, Gopher and the then very new World Wide Web and to me they seemed to offer a really obvious, exciting alternative to desktop published content. I even followed up a visit to Leicester University Open Day by trying to build my own hypermedia system using what was then the new Microsoft Access database, creating what turned out to be a great proof of concept with little practical use.
Several times I put together mini-stacks of content for topics of work for my students that compiled all the learning materials and tasks together. The exercise usually took 2-3 days of intensive effort, allowed me to really get my head around the work we would be doing, they key concepts and questions and the pace needed. In particular, it made me plan various routes and think about differentiation in ways other than simple extension/ substitution.
Positive as it was, on none of those occasions did I see what I hoped for - a group of learners seize the opportunity to self-direct... the material became the backdrop for the topic, I as the teacher found myself setting the waypoints in every lesson and pretty much using the stack of hypermedia as a glorified meta-worksheet. On each occasion I moved onto what with hindsight were more efficient (and more constructivist) approaches.
So hypermedia for me (to date) has been much more about my own learning, my own planning, than it has been about that of my students. Far more effective have been efforts to use tools like blogging to have the learner construct the hypermedia.
Uden puts forward some reasons why learners find working from hypermedia a barrier to learning before setting out good design practice. In particular one concern stands out, cognitive overload.
Cognitive overload is caused by the need for the reader to frequently pause, make decisions about whether to follow links or not, track back and generally build their journey through the material, whilst also taking notes. It represents an increased overhead on the learning process, a distraction from the content itself (perhaps, especially important in an objectivist approach). My own experience as a reader is that hypermedia is extremely useful when I already have reference points and a particular line of research in mind, but I have felt, and observed this type of overload response in practice.
My main interest in hypermedia (now) is as a vehicle for constructivist work. Having the learner construct hypermedia as a way to engage with an area of study. The article goes into a ideas around how to break down concepts, relate them and present them that I hadn't considered in such a structured way before and is something I'll return to when I am next seized by the urge to produce a base of learning materials for a block of learning.