Ian for a first outing with the 20D, I'd say you've justified every penny it cost you, and the short time you've spent on here hasn't been wasted. :wink:
That's a nicely composed shot. That very light area in the sky has just burnt out a little. If you'd checked the histogram in the menus after you took the shot that area would have been flashing away indicating over-exposure. Try taking a copy of the picture, and adjust the levels in photoshop for the sky, reduce the contrast and darken it a little - play with it basically ansd see what you get. Don't worry about what happens to the foreground.Then when you've done, combine the image with your original shot. There's a 'How to' in Tutorials.
Really nice shot- time now to play with it. There's a huge luminance difference there between the sky and the foreground that's a difficult exposure problem anyway. The foreground is perhaps a shade dark, but if you'd given any more exposure for that, obviously the sky would have just burned out even more. When it's like that it's often better to take two shots - one exposed for the sky and one for the foreground and combine the two shots afterwards - the results can be very impressive. Obviously the camera would have to be on a tripod though.