If Zuko and Katara don't get together, I won't care as long as Zuko gets someone fun, like Jin. Mai's just too dull and boring to be paired with Zuko.
If Katara and Aang get together, Ozi better kill Aang. Because I do not want to see some cop-out about the Avatar State saying "Oh, you only have to let go of what attaches you the most to this world for a few moments. Then you can have it again." That would be more of plot killer than anyone could ever say that Zuko and Katara being together could ever be.
Here's another question for all: How do you think your main relationship is going to happen, if it isn't in effect already?
As far as the Katara thing goes, I'm going to say this: She's going to bloodbend again and it's going to be against whoever killed her mother. I think that, since she considers it so wrong, whoever stops her from going through with it and killing the guy will be the one that she chooses. It may be during "The Southern Raiders" but it's definately going to be against the firebender that killed her mother.