Great Channel9 video in GUI testing
I have just watched the very interesting Ifeanyi Echeruo: Testing WPF - UI Fuzzing with InvokeStress. This gives a great discussion of the role of the tester within the development team, and no they don't 'just press buttons to see what happens'. They are there to drive quality and it is very much a development role.
Also it shows how to use the accessibility API in WPF (but similar APIs are there in all Windows versions) to drive testing of the GUI. The tool InvokeStress discussed is also available for downloaded at http://wpf.netfx3.com/files/folders/developer/entry5155.aspx. Basically this tool discovers all the GUI controls and click, drags etc. them to see what happens. This is a great way to check all possible route through an application; but you can also use it to build specific scenario tests.
I really recommend this video to anyone interested in testing quality