Dean's letter reads:
"Sam and Bobby -
Given what's about to happen, I'll be surprised if this package ever finds you. But if it does, I want you both to know that what I'm doing isn't about giving up. John taught us better than that. This is about time. We've run out of it.
Left the Impala in Cicero. Where I'm going, we don't need roads. I know you'll look after her for me. Bobby - you've taken more for the team than anyone could ever ask. That makes you an honorary Winchester in my book.
Sam. You told me once that you pray every day. Not sure if that's still true. Probably isn't, but if it is, give it one last try for me. And Sammy - one Winchester lost to this fight is enough. When it's over [...]"
The number of Dean's hotel room is 100 - this is the 100th episode of the show.
"The Point of Know Return," similar to the title of this episode, is the title of a song by the group Kansas, the performer of "Carry On Wayward Son"
There's a line when Sam tells Adam; "you don't know me from a hole in the wall" ironically the phrase normally goes; "you don't know me from Adam."
When Dean is packing all his possessions in a cardboard box, he addresses the box to Robert Singer.