The new issue of Interactions Magazine (http://interactions.acm.org/) has been released and their main story is Pencils Before Pixels —and I couldn't agree more!
Planning, planning, and more planning, right at the beginning of the process (where it belongs), saves so much time for the people building it and, in the case where a poorly planned User Interface makes it to the public eye, can save lots of end-users time too. Better planning up front makes for a more efficient and effective design.
And the whole idea of designers sketching, with a pencil! a classic method... it's fast, can be collaborative, and it works.