On my 50D (should be the same on the 40D) you can manually adjust sharpness by going to picture style (IE standard/landscape/portrait.. etc) and then press Info to further adjust sharpness.
Having said that - alot of my pictures do have a hint of softness - so far though I have just attributed that to not knowing the camera and lenses fully. Some of the pics though turn out razor sharp so it is definatly my fumbling that is the cause
