This is no big news,not to me, because the signs were always there that something was going on with katara and aang and with aang liking katara, katara liking aang it is only a matter of time when they proclaim thier feelings for one another. They lightly kiss, hug, and are always close to each other and they have a bond that has grown since aang now knows waterbending skills. They will probably announce thier feeling in the next season or two after the battle wtih the fire lord, the series finale, and they will celebrate by plantin a huge wet one on each other leaving sokka speechless.
I think they keep thier relationship, the one thats slowly growing, a secret one because of sokka and two because of toph who likes aang. We will just have to see how this unfolds as the show goes on.