You *may* have a camera that needs to be adjusted... or you may not. :>
Nice thing about digital is that it costs almost nothing to find out. I *love* the learning tool that my D30 is for that very reason.
Take the camera out into the sunlight and shoot a frame filling shot of an 18% gray card. Then look at the histogram of that shot. I'd expect a pretty narrow peak right around the center of the range. I'll try to shoot one myself tomorrow with my D30 - I'm quite happy with the exposure, and I'm pretty critical.
I suspect, but am not 100% sure that you should also get the same results if you shoot a plain white sheet of paper. I would expect the camera to try to turn this to a middle gray shade.
I don't think metering mode should matter in this case, because the whole frame would be filled with gray. Be sure that the light on the card is totally even - no shadows, etc.
In a perfect world, I'd expect you could load the image into Photoshop and see a brightness value right in the center of the range.
By the way, for digital pics, I'd rather have a slight underexposure than an overexposure. With an overexposure, there's no data there - full whites are unrecoverable. But shadow detail, ***ESPECIALLY IF YOU SHOOT IN RAW MODE***, may be recoverable using Photoshop or other image manipulation program.
On the www.dpreview.com
forum, I recall seeing a procedure from a Canon rep for testing your exposure, but I'd expect this simpler method to work fine.
Some people have reported this with their cameras. They've returned them to Canon, and gotten them back adjusted in about a week. I've read several people say that they are happy with the adjustment. I don't recall any that were unhappy. So...bad news, 1 week sans D30. Good news - fully adjustable and fixable.
Good shooting!
-lee-