A cute little trick that might make things interesting, instead of just having a text string for seeding worlds, allow the user enter a file, or use a CD or DVD.
Then instead of telling someone "check out the world with seed BLAHFSDJD35", you can tell them "check out the world generated by this picture of a pony" or "check out the world generated by the Limited Collectors Edition of Friendship is Witchcraft".
Then instead of telling someone "check out the world with seed BLAHFSDJD35", you can tell them "check out the world generated by this picture of a pony" or "check out the world generated by the Limited Collectors Edition of Friendship is Witchcraft".