Science Daily had a writeup about a study which suggests that forgetting things is important to how human memory works. I believe it's possible that we will one day be able to create an artificial intelligence with a perfect memory, but I do not believe that we would be able to consider that AI to be human-like if its memory does not behave as ours does. We will at least require an associative memory, and I believe (with no real reason for believing such yet) that it will be necessary for it to be able to forget things as well. Memories fading and disappearing appears to be part of the human condition; it will be necessary for a human-like AI as well. (Will it be necessary for the AI to be 'mortal'?)