One question my wife asked me when I told her I wanted to purchase a Canon T1i was: we have a perfectly good camera, what will you gain with the new camera?
My answer: THIS.
CP 8800 and 9629 led a train through Indus, Alberta on Sunday evening, after sunset, and I still got the shot.
From past experience, I know that when the sun goes down, the Canon S3 goes back in the bag. It simply cannot shoot a moving subject in low light. Impossible. However, the T1i can do it.
This shot was taken with a shutter speed of 1/400s, aperture of F/4.6, and ISO 1600. The S3 is not capable of ISO "film" speeds greater than 800, and ISO 800 looks terrible on the S3. And this was with the KIT lens!
DISCLAIMER: I did bump up the brightness and reduce the contrast a bit when editing these photos. I was shooting JPEGs, not RAW. They still looked good right off the camera.
Here's the tail end of the train, with CP 8542 giving a shove.
I am very impressed with the T1i's capabilities. Very impressed.