Having participated in some of the Oly I's guilds, I agree that
gm-designed groups add an additional flavor to the game. They also
provide a bootstrap for newbie players to access a repository of
experience/knowledge within a particular domain.
These organization will spring up by themselves anyway. Case in point,
even in the current alpha test a small guild devoted to one of the
magical arts has sprung into existence. Through that group the info on the
entire suite of available spells had been researched and disemminated as
early as turns in the mid-30's. In addition, knowledge, experience, and
pertinent actions are still disemminated on a weekly basis.
The good points to built-in organizations are that they will promote more
roleplay and in-character diplomacy among the members since the
structure is supported from within the world rather than imposed from
without as with the example above and that they will provide that
potential bootstrap that might not exist in an "impromptu" guild.