I think it would be a great idea to be able to see what recipes my guild mates and friends have learned.
What I really want to see though is an in game list of recipes with the names of guildies who are looking for that recipe. This way when you reach a crossroads you can just whip open the guild wanted recipe list and see if you have anything available to buy that someone is looking for.
I would see this as an indicator when you open up the vendor stock list. When you highlight a recipe, you get a list of friends / guildmates that do not have that recipe. When you buy the recipe, you manually send it to the person of your choice and then you mark the name to indicate you sent a recipe to them. Reimbursement would be the responsibility of the other party, as it is now.
It seems like a pretty big thing to implement, though, due to all the possible preferences and tweaking that would be required to make it work smoothly and intuitively.
The last suggestion sounds good, but I dont think its needed to see the recipes your friends and guild mates have learned. The problem I see with the last idea how will the posters clarify they have the $$ for the recipes they want, and what if too many people buy the recipe?? Also, how do you think of implementing this look like?