The change to the way discussion threads are presented is at the top of my list. Check out the difference between the way threads look in Clearspace 1.1.1 versus 1.10. In this screen shot you see the older style on the left and the newer style on the right. The newer style is threaded, and the treatment of the individual messages makes it easier to quickly understand the structure of the conversation.
A more profound change is the customizable Space Overview tab in Clearspace 1.6. By rebuilding the Overview tab with drag-and-drop widgets it became much easier to provide just the right information to visitors in a space. A long list of widgets is available, including some for pulling content in from other systems. Widgets have also been used in several customizations to add new functionality or integrate with other systems.
The "What's New" feed on the home page evolved as well. It started out as a feed of all the activity in the system, but this can be overwhelming in large, active communities. Now "What's New" can be personalized to create our own view of the activity in Clearspace. This change makes it easier to focus on your areas of interest. By clicking on "Your View" you can select only the Spaces from which you want to see new and updated content. This change can decrease the noise in "What's New" so that you can focus on what is most important to you.
Do you have a favorite change to Clearspace from the past year?