I recently bought a 40D in preference to a 50D because...
I have read that to get the pixels on the sensor there have been some compromises in image quality at high ISOs
10Mp still enables me to crop some and yet produce 20 x 24 prints
10Mp converted from RAW in 16 bits to psd/tif = 50Mb file - 15Mp would give ~75Mb file = new PC
So I saved some money on the upgrade, and didn't need a new pc
