I think a lot of the Next own brand stuff is pretty dire but I do think some of the stuff they carry in the catalogue is worth snapping up at the start of the VIP sale.
DS1 is a size 9 in footwear and has a complicated list of footwear requirements for PE including indoor trainers in white, outdoor trainers in white and dark outdoor trainers. I have bought him all brand names in the Next sale plus a pair of converse, all for £15 a pair. I don't know anywhere else I could have done that so cheaply.
In past sales I have also been able to buy Freya bras (normally around £30) for £10 and it has always been that seasons stock that I would have bought for full price in HoF or similar anyway.
I think most of the good stuff disappears in the first VIP slot and that was on Wednesday night. Within a few hours it really is mostly tat left.
Having said that I had a gorgeous and mega comfortable pair of flat jewelled sandals which I picked up for £25 (so already a bargain at full price) when I was taking a short cut through a branch of Next and everyone has been admiring them all season. They went down to £12 in the sale and just had a look and they are still in stock now, admittedly in very small or giant size only. I think people genuinely liked them as a few of my work colleagues have already ordered them in the VIP slots (obviously we've done a deal about not wearing to work or on work nights out!).
I think people massively over order in the first few slots - one girl at work order £800 of clothes! - so if you are interested you can pick up items in a few days from the online sales listing as the returns start to flood in.