I have the 20D, never felt the upgrade to the 30D was worth the money, although the spot metering is useful...
The difference between the 20D and the 40D would be a different matter IMO - The 40D would win hands down. I see at last that the ISO is displayed on the LCD panel 
If my 20D packs up or I feel like spending some money burning a hole in my pocket... 
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