Hi geejay, and welcome to the Camera Labs forum!
The 40D's screen has a resolution of 320x240 pixels, which means when you're viewing at 10x in Live View, you're *almost* viewing the image at 1:1 - ie each pixel on the screen represents each pixel on the sensor.
So you can focus very easily and accurately.
I have a demo of this in our 40D video tour here, and while YouTube compresses the video quite a lot, I think it's clear how well it works:
http://www.cameralabs.com/reviews/Canon ... view.shtml
And check out the astro-photography video to see how it helps with subjects like The Moon...