My father-in-law has a great understanding of the difference between a traditional bricks and mortar company and a modern software business. For example, he once commented that "the value of a software company walks out the door at 5:00 every day."
Most people half his age don't appreciate this point--we'll set aside the fact that 5:00 doesn't mean much in the software world. Clearly, what he was saying is that the knowledge and experience of the people is the most important intellectual property in any software organization. Of course, there is value in the source code and collateral that employees create, but imagine the impact of your staff leaving without any sort of knowledge sharing.
In the past, I have made my own efforts to help prevent the loss of data as I moved from one company to another. At Microsoft, I used the MCMS FAQ as a way of sharing knowledge about Microsoft Content Management Server. When I left, it was just Stefan Gossner and myself working on it--it wasn't a community project, but it probably should have been.
But times have changed, with systems like Microsoft SharePoint taking hold in organizations, social computing can keep that valuable knowledge inside the company. The SharePoint social computing demo discusses the different ways that people share knowledge with MOSS 2007 and the new new methods seem so obvious now--for the MCMS FAQ, I had to write custom code to package the data in a consumable format. However, before I left Microsoft, SharePoint MySites were starting to be used, and the wave of change was clearly on the horizon. Nowadays, I can create a wiki on the Metalogix SharePoint intranet in just a few clicks.
What's coming in the future? Well, details about SharePoint 2010 are hard to come by right now, but there are certainly going to be some improvements. For example, the new SharePoint 2010 taxonomy features will allow users to categorize their information and further remove any friction from knowledge sharing. Instead of your IP walking out the door, it can be blocked at the firewall.