I presented an Adventurer's Guild in the Guidebook to the City of Dolmvay, complete with maps of the compound and notes on its politics, accommodations, services, and how it elevates famous adventurers to celebrity status with the general public. These ideas were taken almost entirely from my home campaign and I have used the various elements over the years.
I'm wondering how many other people buy into the concept of an Adventurer's Guild. I've found it adds a lot to game play and gives me ready hooks for a lot of adventures. However, there is no real (semi)historical counterpart so you're pretty much defining the tone of your game as medieval fantasy. Any thoughts?