What software was used to make the Software Center mockups?

I was reading this Ubuntu Software Center design document and wondering, what software was used to design all those ui concept?

Those specific designs are made by hand by Matthew Paul Thomas on graph paper.

I've found Pencil to be most valuable when I need to pump out quick little UI mocks. It's a Firefox extension by default but you can also get a version that runs on XUL (the framework beneathe Firefox).

While it might not be what was used for this example, it's worth a look.

Mark Shuttleworth uses Balsamiq Mockups for his mockups (like the Window Indicators one). It's not free though.