Ok so I shoot basically one thing....real estate. I am in the market for a new camera so I borrowed a friends canon 50d. I have been using a Rebel xti and been getting good results but I want to upgrade. I took some exteriors today and they came out like crap. Very soft! I shoot with a tripod because i use the AEB functions and layer all of my shots so it wasnt hand shaking. I have a canon 10mm x 22mm lens, set the iso at 200 and f-stop at 6.3. I really dont understand much else and could really use help.
Rodger Cicala over at LensRentals.com would suggest that in fact your lens is not soft, or at least you only have a 3-7% chance of that being the case. You said that you used this lens previously on a Rebel XTi body with good results, and now with a new body the 50D you receive poor results. Rodger contends that this is due to slightly different characteristics that each body can have.
Another great quote to note
It is possible that you have a miscalibrated lens or body, or even both, but a respected(in my opinion) professional with a great deal of experience believes that it is due to the differences between bodies and lenses. A suggested solution would be to send the lens and body combination into Canon and the can properly calibrate the two together.
More could be determined if you could provide sample images. If you find this reply to be the best that you receive, please mark this as the accepted answer.
The 50D supports manual calibration for lenses; therefore it is possible that your friend had it calibrated for their lens, which might be far enough off to impact your shots. (This is assuming your friend has the same lenses, otherwise the 50D would have used Canon's calibrations.)
A few other possibilities, but we we really need to see some example shots in order to give a valid observation: