Upload & Sell: On
If you want some images, I've uploaded a few 100% jpgs here: http://www.pbase.com/rcicala/sigma500
The light's horrid and the subject worse, but I won't have the lens for long -- it's going to shoot the World Series.
Quick summary is it's really quite good at 500 and f/2.8, excellent at f/4. Softens up quite a bit with the 2X converter at closer shooting distances but does well further out even with the 2X. Which makes sense. Assuming that was the plan.