In the sidebar of the Dashboard, there is a filter called Involved people. There you can select to have displayed the operations made by everyone, only by you, only by the others than you, or by a certain person.
The list of people varies according to the project selected. When you have made a multiple projects selection, you'll see a list with all the people involved in those projects. This is a very convenient way to see what a person was working on, across projects.