i saw them two times:
- once before the hype (Agaetis Byrjun just came out, but nobody heard of it here yet)
- once on their () tour, when they were reasonably known.
the first time was unforgettable: a room full of quiet people (a club of, let's say... 500 people?), all stearing in awe at the stage, mouths hanging open, brains flying...
the second time was at a festival, tent-style, but i was kind of distracted by the audience: lots of people were chattering, clapping before a song would finish (admittetly: a difficult thing to know if you're not a fan

), and so on.
preparations? errr... if you're into it: bring some grass along
ps: another fun thing to do with sigur: take out your big headphones, play some sigur ros and wander around in a city where there's carnival going on - and enjoy bizarre scenes unfolding along mindblowing sounds...