Along the same lines as above, an important lesson is that all is not what it may appear to be. Also, a beautiful exterior doesn't guarantee a beautiful interior! Circe, although beautiful and enticing, is not who she might seem to be once one looks at her physical beauty. Her intentions, however, show the reader that she may not be "beautiful" on the inside!
One conclusion or lesson we can draw is one must be very careful whom he trusts as host. She is beautiful, but her actions are not. Without the warning of Hermes, Odysseus quite likely would have fallen into another trap that would have taken a long time to escape without intervention of some other god or goddess.
Like Polyphemus, Circe abuses her guests severely. However, when Odysseus beat her at her own game, she becomes a perfect host. One unexpected event is when Odysseus, while enjoying royal treatment from Circe and her maids, refuses to commune with her in the meal she offers. This is because his men have not yet been restored to him, and are still in the shape of pigs. It is only when she has returned his men to him in human form that Odysseus can he fully enjoy her hospitality, her beauty, and the beautiful surroundings.
The whole host-guest pattern indicates that Circe could still turn against Odysseus or could be completely at his service with the refusal of her meal. Though she is lovely, her maids are lovely, and the surroundings in which Odysseus finds himself are lovely, he must constantly be on his guard as to her intentions and actions.
Aside from all this, Circe chooses to turn his men into pigs, which have never been praised for their beauty. This is a tell-tale sign about the deceptive nature of beauty and her intentions for the men.