The Angel of Memory

This angel appears as nine alabaster-white discs floating just above the ground.  If touched, they give some but won't move from their position.  If a creature stands on one of the discs it will forget something and remember something.  Stepping off and getting back on, or stepping to a different disc will result in the same thing but the process is hazy and inexact, the subject losing more memories each time.
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Stepping on a disc removes a memory and replaces it with one from someone else that has stepped on the angel in the past.  These may be aeons old.  What you remember could be:

1. The place you buried your ill-gotten gains.
2. Those ruins the great wizards go to to die.
3. The place you left the imprisoned djinn.
4. How to use an uncommon weapon.
5. Your signature spell.
6. Your recipe for a toxin.
7. A shortcut that makes travel between two common points half as long.
8. The name of a forgotten god.

What you forget, hmm, I'll leave that up to you.  I was thinking class skills basically, and that they could be remembered as normal be the time the character reaches next level, or sooner if they hire a trainer.  So a fighter might forget how to use long swords for a level but know a spell they can cast from their mind once.

Stepping on the first disc is free, additional cause the subject to lose 100xp per lvl.

I imagine it would be possible that a character would lose something so important to them they might step again and again onto the angel to try and get it back.  To simplify resolving this I might say a new memory is placed in the upper left disc and is shuffled through them with each new memory added.  So, a player has nine tries to retrieve that particular memory before it is rotated into the aether.  It isn't lost for good, because other memories are rotated into the discs each time they are used, but who knows how many thousands of attempts would take to find it after it has left the discs.