This area of research has been explored by Matt Blaze in some detail -- he's done some "good" key escrow systems for just the case of "your chief programmer is hit by a bus." However, let us never confuse voluntary key management techniques used in an organization with mandatory national key escrow big-brotherism. Perry Derek Atkins says:
I have tried to think of a positive use for key escrow. The only thing that I have come up with so far is kind of like having local key escrow within one company, or something like that. Kind of like having a master key that fits all the offices in one wing of a building, or something like that. That could be good in some business uses, provided you could pick your own trusted master key holder. I don't think that is what Al Gore has in mind.
Actually, I can think of one major use. If I encrypt my personal files, I might want my heirs to be able to recover them after my death. For example, I might keep my electronically-encrypted will in escrow, such that upon my death the keys can be obtained and the document opened.