I just imported my entire picture collection and so far things are good. I have a set of about 10 photos that are all about 100k or less. They work fine in the Preview app and show up perfectly. In iPhoto they show up as just black images. When you click on them they come up but it is almost like they are translucent. I have attached a screenshot that shows one of the photos being viewed in Preview and another one after it has been clicked on in iPhoto. As you can see in the screenshot, you can actually see thru the pic and see the other photos.