I as many on this review purchased this lens to improve upon the standard kit lens. I have only had the lens a little while and have taken approx 100 shots with it and confirm a massive improvement over the kit lens. When I used to use the 300d with the standard kit lens I was always post sharpening using software, this is not needed with the sigma, it is absolutely pin sharp. I also have an EF 50mm prime the f1.8 model and can see no difference in shots taken with the SIGMA and the EF prime!
It appears to me that a great number of people frequently try and compare this sigma to the (F4.0)17-40mm L, this makes no sense to me as the Canon equivalent to this lens is the 16-35 L (given the large aperture of the SIGMA). In addition the sigma has the added range of 50 against 35!
So why try and compare a lens worth approx £300 (SIGMA)with a lens costing more than 3 times as much(CANON)!
Judging by the more scientific reviews done on both these lenses and the numerous direct comparison image samples on the WWW, I cannot see £600 worth of improvement with the CANON, and the SIGMA makes a very, very close 2nd place in terms of quality!
This lens is very well recommended for the EOS 300d and at this quality and in this price range Canon has absolutely nothing to offer for the DIGITAL user..
(and as a parting comment, the reduced size of the lens by virtue of the smaller image circle needed for 1.6x sensors it has the added bonus of more portability and a reduced filter size -i.e. cheaper filters-(a circ pol for a the canon equivalent lens is about £150!!!)
all in all a fantastic lens