For quest hints, info, and tips you might like Lightheaded, which is similar to that idea. http://www.wowinterface.com/downloads/info7017-LightHeaded.html
Reread plx: http://www.wowinterface.com/downloads/fileinfo.php?id=5370
That's correct, it's similar but not identical. I'd have preferred to point out something that was exactly like what you'd asked for. I know that Lightheaded is just an in-game knowledgebase, and while the data is culled from the contributions of a user group, it isn't specifically for a guild. But on the other hand, it is currently being supported and it's a good collection of data, although it's limited to quest hints, info, and tips. It's still the only thing I know of that's even remotely near to what GuildBook says it is.