The first step, for us, was to ensure the re-use of content is for everyone to be on the same platform - Many departments were using different software to create content which resulted in less collaboration and more siloed initiatives.
Our solution was to move to a completely integrated system - we chose Microsoft solutions (MSOfice, Outlook, Sharepoint, etc.) We all have the same tools, we can give each other access to each other documents with permissioning, or even share libraries (as in Holly's example with OneNote). What's excellent is that, the MSOffice suite already has many collaborative features - placing them on a Sharepoint site amplifies it even more. Our company is quite large with sites in all of the continents, so we can't afford to play the waiting game when it comes to both marketing, functional, and development content. This solution allows us to be efficient.
The only thing slowing down this process is the dreaded "G" word...governance. We struggle with this too. Everyone agrees we need it but you get both ends of the spectrum - from very "loose" model to an overly restrictive model - when trying to really solidify the model. Under our Knowledge Management Strategy, this is currently being formalised and I must say...we are close to victory.
Using the concept of "Shaping to Framing", a governance model is meant to "frame" - guide, coach, enable and support the content/knowledge - not to dictate what it is, isn't. It is up to the people who own the knowledge to shape the outcome/results within the frame.
Sorry, a bit long winded..but hope that it helps.