UncleCheese,
When I open Safari's Web Inspector I always see this error: Failed to load resource: cancelled Uploadify.swf.
See http://dl.dropbox.com/u/85464/Screen%20shot%202011-04-07%20at%20723.14.52.png
What can this be?
And... while you're (hopefully) looking at this post, can you also have a look at this one (sorry for Hijacking your attention): http://www.silverstripe.org/general-questions/show/16475, as I think this topic is in your area of expertise.