So, with those initial personal reservations, I go into the Pathfinder Chronicles book, Seekers of Secrets which details the Pathfinder Society, the biggest, most organized Adventurer's Guild ever concieved (to my knowledge) for any D&D campaign setting.
I can't say that Paizo completely removed all my reservations about the concept; quite often, the stuff this book described felt very artificial and contrived to me; clearly game artifacts rather than something that actually makes some sense to exist in a typical fantasy setting. There couldn't be anything like these Adventurer's Guilds in Hyboria or Newhon, for example. And yet, Paizo did manage to make an Adventurer's Guild that felt sufficiently well detailed and explained that I could at least justify it.
The Pathfinder Society is, in a way, Paizo's eponymous organization in Golarion, their world, the society that's named after the entire gameline itself. And it's sufficiently broad in scope, that it makes some sense. One thing that I've really liked about Golarion is that it manages to bring back to D&D that tone and feel of the old pulp stories. Doc Savage, Tarzan, John Carter, Conan and Kull, and the rest of them... they clearly feature echoes all throughout the setting. The opening up of Osirion to treasure hunters is another hint: this is a world of pulp action of the type that could take place in the early twentieth century of our world. And in that vein, the Pathfinder Society is largely made up of folks who bear a resemblance to Indiana Jones and his rival Rene Belloq, or Rick O'Connell of The Mummy, with more studious types perhaps being more like Rick's love interest, Evelyn "Evy" Carnahan. This is actually a model that works to some extent. And the organization itself is full of plenty of adventure hooks to potentially allow players to pursue. Like Indiana Jones, the implication is that Society members aren't heroes; they resemble the real life prototypes that Indiana Jones might have been based on; the Roy Chapman Andrews and Heinrich Schliemanns of the world, adventuring, exploring, treasure-hunting... and hopefully doing at least a little bit to advance the cause of human knowledge in the world while they're at it. Evil, selfish characters who engage in all kinds of shady dealings make up a large percentage of Society members---as long as they bring stuff in for the Society, catalog new places, and generally contribute to the mission statement of the society; the advancement and dissemination of knowledge.
So, although I thought I wouldn't really have much use for this book based solely on the scope of it (I bought it as much for the cover art as for any other reason), I found that it actually did detail an organization that could potentially be very useful to me, even if I dislike the idea of "adventurer's guilds" on principle.
One thing that I was surprised, and a bit disappointed at in the book, though, was that it spent page after page after page talking about ioun stones. I guess I somehow had not picked up from my prior readings of setting material, that ioun stones were supposed to be strongly associated with the society. To me, ioun stones were these very weird magic items that were very flashy in appearance, and screamed "not really sword & sorcery" to me. I've never been a big fan. So, after I while, I found myself starting to skim just a bit... the ioun stones got way more coverage than they deserved here.
Otherwise, though... it detailed a lot of interesting NPCs the PCs could interact with, some interesting locations, lots of potential plot hooks, and an organization that actually takes a nonsensical idea and attempts to make it make some sense. Not a bad investment at all.