I am aware of sensor crop, and I thank you for offering that information in case I wasn't.
However in general, most lenses lose sharpness toward the edge of the full frame (especially wide angles and even more especially so this lens, as seen in the MTF chart below), so in one review I read (which was in fact performed with a Canon Rebel XT), it was noted that the lens was surprisingly unsharp in the corners until stopped down to f/5.6 I believe - which was somewhat unassuring since it should perform even better on an APS-C size sensor due to the sweet spot effect, and also considering the lens' price tag.
See the MTF chart on Canon's website, which will hopefully show up below:
http://consumer.usa.canon.com/app/images/lens/ef_24_14mtf.gif
Thanks for your help though and if you are ever interested in this lens later down the road feel free to ask me what I think of it as it should be arriving today.