I ended up with this lens as part of a lot of digital equipment I purchased a few months back. After selling the items I didn't want, this lens turned out to be a freebie. A rather valuable freebie at that. It is a good copy, any picture I shoot at f/6.3 or smaller comes out razor sharp...unless I am the one making the mistake.
Compared to the kit lens, the Sigma 18-125, and an old style Canon 22-55 lens I had, this lens, when properly shot, blows all of them away. Color, highlights, and sharpness are all excellent. 24mm (on a 1.6 crop) is wide enough for the type of shooting I do, and 85mm (really about 136mm) is generally enough reach for me as well. It is a fine walkaround lens, and can easily be carried around all day, especially on a Rebel XT body. I have read in various professional reviews that this lens on a film body was never particularly popular because of soft and dark corners, but it really shines on a crop body because of first rate center performance. The pictures I get with my XT seem to bear that out.
Pictures can be soft when shooting wide open, and the zoom definitely moves if it is tilted much past 45 degrees or so. Also, 24mm (38mm equiv) may not be wide enough for everybody. However, those are weaknesses I can live with. Even at the normal price of $300, this lens is a fine deal. For what I "paid" for it....it really works out well.
This review is based on a crop body, if you have a 5D, you might want to read some professional reviews on the corner performance for this lens.