I've ended up thinking about the different ways that I've heard 'open' being used around content specifically (leaving aside open source and 'open technology' at this point), and about which I think we need to know more (scare quotes alert!)
'Openness' as a feature of communities/organisations: What features of educational communities and institutions could be described as 'open', or precursors to full participation in 'open content' sharing?
'Openness' as a feature of content: What features of content allow it to be fully shared and reused in other contexts? Are these features enhancing of or inimical to specific pedagogical values (e.g. those which are strongly situated or context-based)? What are the implications for quality processes?
'Openness' as a value in education: What impact is 'open pedagogy' having, above and beyond issues of content, and how should we understand and promote this idea?
'Openness' as a feature of certain technology-based services (typically public/third-party): Are web 2.0 solutions to content hosting over-riding the demand for deposit of content in 'open' repositories?
Since first writing this post I've also been reflecting on the links - not nearly strong enough yet IMO - between open content and open access to research materials. In the US a new Compact for Open Access Equity, signed by 5 leading HEIs, commits them in effect to supporting open access publishing by their own staff, on both economic and scholarly grounds. What would leadership of this kind look like in relation to educational (T&L) content?