BN: I bought a macbook air for work 2 months ago. It was awful - couldn't cope with video calls without the noisy fan kicking in, really slow switching between apps, laggy in excel and powerpoint. Phone support was well meaning but didn't actually change anything.
GN: Went into the apple store over the weekend and within 5 mins of talking through the problem she agreed it wasn't working out for me the way it should be and swapped it for a macbook pro completely free, even though it cost about 300 quid more. She did all the data transfer too. It's been great on this mornings video calls and havent heard the fan once yet.
I suspect there are 'known issues' with the noise of the fan of the Air, so worth a trip to the store if you're suffering too!