So a friend of mine is working on designing a game he's calling Shadows of Azathoth. There are a lot of neat ideas going on here, but the ones that interest me at the moment are that memory is priceless and memory is unstable. With his permission, this post comments on some of his neat ideas, and how the design could be tweaked to correct some unforeseen oddities.
During character creation, each player specifies a list of memories. The first is Identity, rated at 5 (more on ratings in a bit). If your Identity rating drops to zero, you have lost all of your sense of self and gone irretrievably insane. You also have Upbringing and Training, rated at 4; Important Person, Best Memory, and Worst Memory, rated at 3; and six slots for Other Players, all rated at 2. It's okay to completely lose memories other than Identity, but they're definitely worth maintaining.
Memories are rated on a scale of strength from 0-5. (Without getting too deeply into the conflict-resolution mechanics, I'll mention that it's a d6 system where 4+ on a die is a success in normal circumstances, but sometimes only 5+ or 6 is a success.) When making any roll, a character can draw upon a memory to improve her chance of success. (It would be good to clarify whether the player declares this before or after the roll.) She receives a number of points equal to the memory's current rating to distribute among the d6s rolled. She might spend three points to bump a 2 and a 3 up to 4s, making them successes. The rating of her memory then temporarily decreases by 1.
At the end of the session or adventure, the player rolls Willpower (one of your core skills). For every success, she restores one point lost off of an existing memory. For every point she does not successfully restore, she forms a new memory, keeping her at the same total number of points of memories. This new memory is likely to have a pretty low rating.
During play yesterday (the first session!), we saw how this actually worked out. I used two memories and recovered one from Willpower. The other point became a 1-point memory of the mission we had just accomplished.The problem with this is that a 1-pt memory is much less useful than the 3-pt memory that got reduced to a 2-pt memory. Honestly, a 1-pt memory is scarcely worth using, and if I'm figuring out how to spend my Willpower successes at the end of the session, I am definitely not going to bother retaining it if I have any other options. (Declining to retain it will cause it to be replaced by another memory of rating 1 or higher.) As far as I know, once I make a Willpower check, any "temporary damage" to memories that I do not repair becomes permanent and irreparable by anything short of plot intervention.
Understand that this is a game about hard-bitten (and frost-bitten) soldiers in big spaceships traveling from planet to planet, and going into cryo-sleep to endure the long journeys. Cryo-sleep does terrible things to one's memories over enough cycles of freezing and thawing. It is therefore setting-appropriate that characters start with a smaller number of clear, strong memories and gradually wind up with a large number of weak, dim memories. The exact form that this takes within the rules might be possible to improve, though.
I can imagine doing this a number of different ways. I would start by making it possible to have more or less than 35 points worth of memories. Failed Willpower rolls don't result in new memories. Instead, new memories are a reward from completing missions. The characters of yesterday's session might now have a new 2-pt memory: Formalhaut 2. Dr. Kensington's memory of this place might be mixing up a batch of chemicals to create the defoliant that saved the colony, while Miss Carne's memory might be of beating the moss-covered technicians to death with a mono sword. Future missions might be 3 or more points, and optional victory objectives in the course of a mission might increase the number or add additional memories. Old memories fade through use and failed Willpower rolls, or each round of cryo-sleep might force us to lose a certain value of memory rating (or there could be another Willpower check).
I'd consider a more purely memories-as-Sanity system as well. When a character draws upon a memory, its rating does not decrease, but it is exhausted until the end of the session. When a player takes Shock (damage to mind) in excess of (3 x Willpower), they can spend permanent points of memories on a round-by-round basis instead of spending Effort to stay in the action. I'd add a pretty nasty Shock attack to the process of waking up from cryo-sleep, with a table of obscure modifiers. Memories lost in this way might be restored by the Therapy Module, or the Therapy Module might replace them with something completely different. There should be a chance (or possibly a guarantee) that memory loss results in horrible Mythos memories and dreams.
Somewhat Off Topic
This is one of the best systems imaginable for encouraging players to keep in-character personal logs. They are quite literally working to shore up their memories, and extra Willpower tests to strengthen existing memories would be cool. Audio recordings might be even better.
I am interested in seeing where this game goes in the future, and I look forward to times when unstable memories cause strange and complex roleplaying considerations.