I sold my 3 month old Canon "Digital Rebel" 300D. Upgraded to a Nikon D70... and what a huge difference that was.
I do find the pictures that are produced with the D70 sensor not as high in detail under some conditions, however I must say that overall they are at par. The "big difference" comes in the rest of the camera.
The interface makes it far quicker to access control options and the camera itself is faster to react -- no more missing shots because my daughter wont sit still -- and I can just shoot freely without checking if the memory buffer is full (my Rebel sometimes became unoperational when it was saving data to compact flash).