It's definitely doing correction, I think it's just not doing it perfectly (probably my lens distortion doesn't exactly match the Canon's). And maybe I moved some. :)

(It was more obvious in a couple of non-posted pictures, like the picture of the doorframe, merging the rightmost photo from
top (http://web.mit.edu/boojum/Pix/Move/photos/photo_6.html) and bottom (http://web.mit.edu/boojum/Pix/Move/photos/photo_7.html) and the door looked straight. I was very impressed. )