Kalani being the rat: sounds extremely complicated, somebody laid down a credible scenario earlier in the thread and it was very long and convoluted:
he'd have to be a spy BEFORE ending up in the arena, he'd have to know already that the mallers had issues with the guys in the tower, he'd have to be like "oh, good, by extreme luck I happen to be rescued by the guys I overheard the mallers have trouble with, let me be the rat then." etc
Plus, how stupid would he be to write "BTW, I'm a spy, but don't read this or you'll blow my cover" on his diary?!

I don't think he was informed about the redhead at the golf park during the flight back:
- "it's a redhead it must be her omg I wanna die kthxbai boom"
- it all happens "off camera", so to speak, and that would be extremely lame. Show, don't tell, and we aren't shown anything on Michael briefing him about the girl in the park, we are just imagining it. It would be a key scene and I just can't believe they would let it happen in the background.
I instead think the story with Kalani is something else entirely and we will be shown what "Hannah" means in the future when Angel or someone else reads his diary.
(Also, without the forums there was no way I could tell he said "Hannah", I listened to that part over and over, and I had trouble understanding Tar saying "Pippin" too. I'm not a native english speaker but it's the language we speak at work. I want the scripts together with the episodes on iTunes, too! :P)

Another thing: I guess the actress playing Tanya wasn't available. At least I hope so: there was a huge expectations buildup during the past episodes: "I think I know what the rat is", then she is attacked by zombies, we fear she's going to turn and then *poof!* all of a sudden she's up and walking about, and it all happens off camera (which, now that I think about it, is a good argument for Kalani thing happening off camera too). For crying out loud, I don't even recall hearing her voice the whole episode, it just suddenly goes "Oh, and fyi, there's Tanya on the chopper too" at the end.

Cuse and Lindelof said they would answer all the questions at the end of Lost too, and look what happened... between Randy, and Michael's arm, and the rat, and now this Hannah... I just hope it doesn't go the same way as Lost.