Ha .. I was just about to ask for the EXIF .. Thanks... Wow 30D ? great shots... the first two are tiny bit soft probably light not helping.. but don't take my feedback to heart I'm no expert. I'm wondering if the 1.4x isn't begging to be stopped down further? *(should be able to go one more stop with the lens being IS?) The other photos you posted were spot on IMO maybe just the lighting on these.. I can imagine a non crop (full frame) sensor would be awesome with that amazing lens !
Now that I look again... perhaps some focal point issue? Looks like the focal point on the first few is on the duck's back? Hit 'em in the eye ! You do good work !
Thanks for sharing !