Villagers are the only mob that can be interacted with (beyond killing it), and Minecraft 1.8 will have improvements in store for them. Today on Twitter, Jens said "Been rebalancing villager trading in Minecraft. Offers will be less random and probably more useful." He also shared that spawned villagers that the player has traded with already will not change in 1.8, since their trades have been written to the save file. Unfortunately that's all Jens or any Minecraft dev has said, so we are left in the dark about details. Let us know if you are interested in enhanced trading in the comments, and see the source link below for the original tweet.
Source: Twitter