The support band was one Amina Strings, who are also from Iceland and have played and collaborated with Sigur Rós quite a bit (I recall seeing a flyer for a gig they did up in Scotland some years ago). Four women who seem to be a string quartet who picked up other instruments. Their set involved them playing various sorts of string instruments (including violin/viola/cello and some sort of harp/koto-like ones), plinking away in synchrony on chromatic percussion, playing a saw with a bow (think Delicatessen; it makes one wonder whether it was an ordinary hardware-shop saw or whether there's a place somewhere that sells special tuned saws for musical use), doing various things on an iBook, and bringing out a Casio VL-1 at some stage, set to Rock 2 (that's the Wöekenender loop). They weren't all that far from Múm territory.
Next up there was half an hour of weird, glacial drones played through the PA as people went to buy overpriced Carling lager in plastic cups. (Aside: Carling is rubbish; it's not so much a generic beer like Carlton Draught, as a homogenised, heavily carbonated piss; probably a similar concept to the US Budweiser, which I've so far managed to avoid. Carling, however, own the live music scene in Britain, and are harder to avoid.) Then Sigur Rós came on. The first thing I noticed was the frontman playing his guitar with a bow. Not one of those E-Bow magnetic devices, but an actual cello bow. The guitar in question looked very traditional, redolent of the blues/rock heritage of the American south; the juxtaposition of it being played with a bow seemed rather postmodern. That's not the only weird thing he did with his guitar; at one point, he held it to his face and sang into the strings.
Sigur Rós played for about an hour and a half, including two encores. They were accompanied by Amina Strings during some of the songs. They played some old favourites (including Svefn-g-Englar and the first two tracks of ()) and what seemed to be some new tracks. One of them sounded a lot more approachable, and almost like a Doves track; perhaps it's a consequence of them having signed to EMI? Anyway, the light show was pretty good too, with the colours (deep golden greens and icy blues) and visual projections (ghostly processed images of moving people and jerky video of electric pylons) going quite well with the music. More photos here.