I've had some problems with this.
They definitely allow you to get the full HE discount instore with a NUS card, two of my friends walked out with MacBooks for £600.
However - when we asked them about the 3 year warranty they said it was online only. We showed them webpages about the HE 3 year warranty but all the Genius' were adament that when bought from the store it only comes with the 1 year warranty. But you can buy Applecare for about £50 instead of full price. Might be worth checking up on/bearing in mind.
I'm sure you wont regret it whatever you choose.
