Binding to ComboBox.SelectedItem through a custom dependency property

Since early 2001 I've been working full time as a software developer and since 2004 I've been working mostly with Microsoft technology.
I started out as a product developer, but after a few years I switched to a project company where my roles ranged from developer up to consultant and from team lead and coach to manager.
Eventually I switched jobs and focused on the consultant part and then I got back to building a product once again. Now I work in a job where I get to do both.