I kept getting a memory_limit error when importing my attachments. The error didn't make sense considering the file sizes I was dealing with. So I debugged it to see exactly which attachment was causing the error. It was a 793 byte gif. You can't get much smaller. Then I went to the post to view the image. It was a blank gif image with dimensions 640 x 60887.
The image library was trying to thumbnail that sucker and ran out of memory.