I hate threads on my own site that aren't resolved, so I'm posting an update to this one...
Cureved surfaces are going to have "jaggies" -no way around it. But you can reduce the severity by using a mate color that matches the background that the graphic will be displayed on. So the jagged areas just sort of blend in.
I also changed the default color for the body property on all of my style sheets to the same color I used as the background color for the graphic. Since I used a neutral shade of gray (#e6e6e6) it blended in with all of the default styles that ship with Threads.
