Here Castiel is in a homeless shelter and soup kitchen. In real life, Misha Collins actually volunteers at soup kitchens and homeless shelters.
This marks the first episode where they actually show an angel possession throughout its entirety. Usually they only show the bright light appear and cut away until after the fact. Ironically, an angel possession isn't all that different from a demon possession (visually, anyway) in the sense that the only difference is that the Angel smoke is white.
In this episode, Castiel goes by the name Clarence (the name Meg used to call him). Clarence is the name of a character (who happens to be an angel) from the movie It's a Wonderful Life (1946).
The title of this episode (I'm no Angel) shares a name with a music single by The Gregg Allman Band.
Castiel walks through Chinatown. Supernatural is filmed in Vancouver - a city with a large Chinatown and a large Asian population with a rich history.