I did this a couple of weeks ago, while avoiding real work. But since then, I have been too busy with real work to actually post this.
As a GNU/Linux user and computational scientist, I spend a lot of time looking at computer screens. So a while ago I decided to do the transparent terminal thing, so I could see my background while I code. Keep things spicy rather than looking at white-on-black ALL of the time.
Most people (sub-human kernel hackers, really) choose their backgrounds as either softcore porn, or softcore hentai if they are *really* nerdy. However these pictures tend to be flashy and interfere with you being actually able to read the text. So these people (see above) have to actually decrease the overall transparency.
I go with simple, mostly black backgrounds. And I require that the color scheme in the picture *does not* interfere with the default terminal color scheme (Yeah Gentoo!).
This more or less means that I have to make my own backgrounds since it is impossible to find pre-generated images that satisfy my needs. I still go with the traditional anime theme, though not quite as slutty.
My previous background from last year was for GTO. My new background is of a new type of hero.