Greg Egan is one of my favorite authors. Several of his fictional works have dealt with the idea that all possible universes exist. His latest story "Oracle" is about Alan Turing in an alternate history of our universe. Here's an interesting quote:
"Now I know you're lying!" he shouted triumphantly. "If you believed everything Stoney told you, how could my choice ever mean a thing? I would always say yes to you, and I would always say no! It would all be the same!" --- The full text is available at http://www.netspace.net.au/~gregegan/MISC/ORACLE/Oracle.html. You might want to read it first before proceeding to the next paragraph. Writing fiction that explicitly assumes the AUH seems rather difficult. The way Greg Egan deals with it here is to posit the existence of a technology that can prevent coarse-grained histories from splitting. It's not very satisfactory to me since such technology seems to contradict the AUH. He takes different approaches in his other works; none of them are fully satisfactory, but the stories are interesting and entertaining anyway. Egan also talks about the equivalent of a Rapidly Accelerating Computer (search the archive for "RAC" if you didn't follow the earlier discussions) in this story, hence the title. I'm not sure why he brings it up though, since the consequences of the existence of the Oracle are never examined.