I agree with The First. I absolutely loved this episode! From the moment I saw the words 'Written by Rebecca Rand Kirshener" I knew I would love it, and I did. She's my favorite writer on the show, other than Joss and I loved all of her eppys so far.
I too was wondering what happened to the other SIT. I was happy with the twist ending, Dawn being a SiT is just too cliched for me. I actually like Amanda. She didn't get the job based on her looks, and she plays her part well, although she was very skinny.
The exchange between Xander and Dawn at the end was excellent. very nearly one of my favorite moments of the season, it almost had me in tears, but I'm a sap so hey!
I have a theory about the next Slayer though. I still think it will be Dawn. Buffy was never an SiT remember and Joss likes to surprise us as seen in this episode. What better to have someone not even an SiT becoming the nest slayer, although I'm not sure if I'd want this since the exchange between her and Xander would be less meaningful in a way. My money is still on her becoming the nest slayer. Please note, that that is not a spoiler. Just my speculation. 😀