Was that just in the early prototype? The bulk at the back of present design looks OK to me: http://www.google.com/glass/start/what-it-does/ (3rd image from the bottom). Just going by appearance, there are ordinary sunglasses with a similar bulk. And the compute unit will only get smaller year by year.

I'm actually kinda amazed they've managed to make it that small - OTOH, I see the key point of the project is a way to make hardware smaller yet still be usable (because we don't need a large screen).