Some thoughts:

Nikki/Jessica: I don't think that the dual personality thing is part of her power. Because what the hell kind of power allows you to absorb the personality of a dead sister? More likely, Nikki is someone is who is actually mentally ill (Dissociative Identity Disorder) but in ADDITION to her mental instability, she also has super human strength. I think the super strength is her power, the dual personality thing is just a normal psychotic break that probably resulted from the abuse of her childhood coupled with the trauma that came with the death of Jessica. So now we've got a super "hero" who is actually mentally unstable. Cool.

Hiro/Charlie: I am very sad that Charlie did not stick around to become a regular on the show, because her power was probably the one I admired the most. On the issue of Hiro and the time-traveling business. It's all pretty ridiculous. So many holes it might as well be swiss cheese. So yeah, I'm not even gonna get into all the paradoxes involved in Hiro's time-traveling because apparently, the writers aren't thinking about it as well. Let's just say I'm pretty disappointed with how they're carrying it out. And no way, no how can a Japanese guy who has lived his entire life in Japan come to learn English so quickly, and not only that but it is one of the most difficult things to lose an ACCENT so quickly. It might be possible that Hiro is just a natural at learning English. That's one thing. But to lose the Japanese accent so quicky? It's ridiculous and it takes me right out of the scene when he speak with near perfect English like he did right before Charlie kissed him. Also regarding the kiss, BOO! You hardly ever see inter-racial kissing on network TV. Let alone an Asian man kissing a white girl. Sucks to be Hiro.

Big Brother Petrelli: I loved the scene in the car. Talk about fight or flight response! Dang, that was great. It also explains pretty clearly why he's such a huge asshole and why he hates his ability so much. I mean imagine the guilt he must carry after what happened. He saved himself but left his wife to crash. Whether this was completely involuntary and instinct just took over, or some part of his mind knew he had to choose self-preservation over anything else, that must be quite a load to live with.