Dawn and Faith recognize each other, despite never having met before. This is further demonstration of the spell that the monks cast in Season 5 to make everyone in Buffy's life believe that Dawn had always been Buffy's sister.
The trivia items below may give away important plot points.
Joss Whedon briefly toyed with the idea of killing Xander in this episode, and having him appear as the First to Buffy for the remainder of the season. However, he decided against this because Xander was the one character who never wavered in his loyalty, and doing so this late on in the final season would not leave enough time to properly deal with his death. He ended up having his eye gouged out by Caleb instead.
Just before the confrontation with Caleb, a potential slayer notes that his residence looks like "an evil vineyard", to which Spike responds, "Like Falcon Crest." Falcon Crest was a CBS soap opera in the 1980s that revolved around a wealthy, feuding California family who made their money from the wine industry. This reference also reminds us that Spike is a fan of soap operas.