You didn't look at the photozone reviews before you bought it?
Canon EF 16-35mm f/2.8 USM L @ 16mm:
http://www.photozone.de/images/8Reviews/lenses/canon_1635_28/16mm_distortion.png
Sigma AF 10-20mm f/4-5.6 HSM EX DC @ 10mm:
http://www.photozone.de/images/8Reviews/lenses/sigma_1020_456/10mm_distortion.png
16mm on FF would give you the same field of view as 10mm on a 1.6x crop body, right? Given my experience with my EF lenses on both the 40D and film Rebel, I would say that for the same lens, barrel distortion is much more pronounced on the full frame. For example, the 24-105 shows hardly any barrel distortion at 24mm on the 40D - at least not enough to be easily visible in my photos, even architecture photos. But on the film body the distortion is fairly apparent. Enough that a lot of the guys on the 5D/1D forums call this lens "poor"