Well, one of the most common problems are the images at the basket step(s) on SSL with usually low cache hit [ratio]. Servers end up doing routing for static content and backend content, adding complication to the architecture and for content editors. If you can place the images on SSL on the CDN it is much easier and you need less content servers.

The details vary significantly on each scenario. But as a global service I think Amazon will eventually have to add SSL, IMHO.