This is the main background image
http://www.autemo.com/styles/img/background.jpg
it's 25kb. The black background is not an image, it's just a colour style (<1kb).
Your web browser is made to cache websites that you visit. It does this to make it faster to load up the page (and save bandwidth) each time you view the webpage. So turning off the Autemo website styling won't make any significant difference at all.
Viewing everyone's signatures, and high-res chops does use up some bandwidth however. As choppers typically post high res chops anywhere up to 1Mb. So if you're concerned about saving bandwidth, be mindful in particular about how many images you view here and on other places on the net.
That and also stay from sites like youtube especially. Average length videos on there are typically upwards of 10Mb..