In thinking about the GMail encryption problem, I came to realize that for ordinary users liable to forget their passwords, it would not be suitable to tell them after such an event that all their email archives are forever lost. This means some sort of Key Escrow. Not the nasty kind done with the clipper chip, but one done voluntarily.
I came up with a system I call Friendscrow. (I suspect others have also thought of the same thing.) This is a ZUI (Zero User Interface) system, at least for normal operation.