Why am I having this problem importing photos from iPhone to iPhoto?
I seem to have resolved the issue by connecting my iPhone 4 directly into my MacBook as opposed to using a USB hub which I connect everything to.

edit: I also found this to be the case after a long term problem with importing photos/films from my iPhone 5; it was intermittent and buggy, but I was using a simple USB extension cord from behind my computer and eventually removing; because of this, this answer solved the entire issue.