Google Presentations now with custom backgrounds

I love the ease of use of Google Presentations, part of Google Apps, and – more importantly – part of Google Apps for Education. When it was launched, however, the number of themes available was rather limited. You ended up with incongruities like this (from one of my students):

At least now some customization is possible. According to the Google Operation System blog, 800×600 is the recommended resolution for background images to your slides.