No, graphics aren't that heavy on many pages and they aren't coming from background attributes in an external style sheet.
Sometimes, if cache is cleared, the page will load without the "white flash" and other times it doesn't make a difference if the file has *ever* been loaded in the last week - it still has a flash. But, it always has a flash if I 'reload'.
Just having a look around the Web-- It certainly doesn't seem like a global Opera problem...which is why I have to wonder what's causing the problem. It was happening in 6.03 on one particular case site as well.