I often use this opening as black

1. ... b6 is Owen's Defence, but I think you get out of book pretty soon.

Agreed. In some top-level games, double fianchettoes occur, but only because either

a) You are ahead in development/have tempo or;

b)You're opponent is completely binded and you can develop freely

You can't blanket-label the double fianchetto defenses as simply "too slow."  They get use up to and beyond the 2700 level.

What they are is "too slow unless you are REALLY good positionally and tactically."  If it's really your favorite, by all means carry on with full awareness that what you're playing is perfectly sound, but extremely difficult.  (And much harder to play, than to play against.)

You can, however, work up to a position in which both bishops get fianchettoed. It's just that baldly playing ...b6 and ...g6 is neglecting too much else in favour of getting the bishops going. In the game in the OP, White was much too helpful by playing 4. d5 - he should have kept both pawns on the fourth rank and concentrated on piece development, which should have seen him well able to build a strong centre. No need to get the rush of blood to the head and start charging forward before he was ready!

looks kinda like a hippo to me

HAHA OMG U SUCK :P:P plz, I can beat you anytime :S :v

Lol actually, i play an oppening which uses double fiancheto as black, never tought about that, but the dragadorf uses double fiancheto