Jonathan,
I see from your gallery you have Nikon & Canon, and top glass so I post this link to a run off between The D2X and 1DS MkII.
http://www.naturfotograf.com/index2.html
Scroll down and the link is in the centre section.
This is where you enter new territory for web posting. If the image is full frame, and contains lots of fine detail, then you have to apply nearly maximum compression in ps to get a reasonable file size. That level of compression destroys the fine detail making some images unpostable as they just look rubbish. SeanKP's has found the same thing from his comment on the shot ' Cairo Cityscape ' taken with the 1DS MkII. Without compression the detail in that shot would be amazing.
Don