The King's Indian Attack is a very reasonable opening and was employed by none other than one Bobby Fischer in several games.
A couple of good points include the following: a) allows one to get several moves into the game without being skunked by some sharp tactics, b) allows system playing to a certain extent, and c) allows one to learn the 1.e4 e5 lines while not having to play mainlines against the semi-open defences. On the other hand, Fischer himself would not play the KIA against just anything, preferring it against specific lines by Black.
One would think: Oh, if the KID is so good for Black, then the KIA ought to be really great with White. Turns out that most reverse Black openings do not confer any significant advantage to White because he/she has not profoundly useful purpose for the extra tempo. Still, the KIA is surely sound enough to play at nearly every level of chess, so keep using it and scoring your wins.
I often use this opening, but I don't ever see anyone use it. I think it is great because of the openings for attack that you create without weakening your defenses.