So, my solution is to set up a GeekTool window that does nothing, and drape it from the top of the screen to the end of the Terminal.app title bar. Set it to the colour of your chosen background, and make sure it is set to always be on top. I found I had to get rid of the battery and speaker icons from the menubar, as they would otherwise show through.
I have my GeekTool window set to show the output of entering nothing on the command line every hour or so. You could have it read the file /dev/null instead, I guess. I personally use a black background with the text colour changing according to my mood, or the time of day, or whatever. I use a 80x26 window that takes up the whole of my 1024x768 iBook screen, since I use Bitstream Vera Sans Mono set at whopping 21pt. This setup works well in combination with the utility screen, a nice alternative to having many shell windows open.
Since in this specific account, I have Terminal launch in place of Finder, I use it as a dedicated CLI session account. For working in Aqua, I'll use another account. It's like the >console login, only with your choice of colours, fonts, and the added bonus that it won't mess up your computer after five minutes.

