This camera offers a few well considered improvements over the 20D it replaces. The sensor and processor are the same so the image quality will not differ one iota, BUT an enlarged LCD monitor, spot metering, vastly improved shutter life and ISO displayed on the viewfinder are worthy improvements easily justifying the upgrade from the 20D. If one is considering an upgrade from the 10D my advice would be to definitely go for it. The 20D and 30D both have the "instant on" feature and this represents a vast improvement over the 10D. The 10D was felt by many to have focusing issues and though I did not have any significant problem with my 10D in that regard the 30D represents a substantial improvement in this area. Canon still is not offering (in this price range) a camera with eye control or 45 focusing points, BUT the nine focusing points that ARE offered are well placed and the camera focuses quickly and surely resulting in tack sharp photos.
The pictures this camera takes are simply beyond belief. Beautifully saturated, tack sharp, NO, and I mean NO noise at 400 or below and barely discernible noise all the way up to 1600 ISO. For all practical purposes 1600 ISO is an entirely usable speed resulting in fantastic pictures. What Canon has accomplished in reducing noise and increasing pixel density proves that they are, for now, the technology leader. Canon for now is doing a better job at controlling noise than Nikon though Nikon with the D200 comes pretty darn close except at 800 ISO and above.
The new flash system, ETTL II, available first on the 20D is a vast improvement over previous systems. The in camera processing results in exceptional and pleasing pictures. This camera has a fixed continuous shooting rate which was not present on the 20D. The megapixels stay constant at 8.2 million pixels. Many may be disappointed that the MP count was not increased and feel that perhaps a nominal increase to 10MP would have better justified an upgrade. Canon obviously feels that noise and other features are more important at this point than raw MP's and I would agree. The holy grail of digital photography is now dynamic range. And while this camera offers no improvement in dynamic range I think we can expect to see such improvements in future offerings from Canon and the other manufacturers.
One of the greatest things about digital photography is the ability to build a digital dark room for next to nothing. With the included Photoshop Elements you are well on your way to producing pictures that you could only have imagined in the pre-digital days. I am able to recoup pictures that I never would have considered salvageable before this camera. And while Elements is a great program and more than adequate for most needs I would recommend considering Photoshop CS2 for those who intend to plumb the depths of this hobby.
Another thing I like about Canon is the lens system which IMO is second to none. Also, Canon continues to innovate at a furious pace driving the price of these digital cameras relentlessly downward. This camera is being introduced at a lower price than either the 10D or the 20D. The 5D is plummeting in price and is approaching my "strike point" for purchase. I expect that we will see a sub $2000 10 MP camera with a full frame sensor in the next 18 months. Such are the economics of digital photography. It would seem that Moore's law is driving the prices down inexorably.
So, I LOVE the 30D! LOVE Canon. And LOVE digital. All in all I'd say I'm a pretty happy camper!