I usually shop early but I am at a more organised stage than I usually am this time of year so I am happy.
To the person who asked about how you know what people want early, I start with those people who are consistent. My older son is autistic he has very set, specific interests. He doesn't ask for toys, wouldn't understand the concept of choosing something from an advert or the Argos catalogue. So it is easy to buy for him early and know it will still be something be loves.
My younger son is very little, too little to ask for toys. I just see what he plays with and what he most likes.
My husband does a wishlist, he has a fairly unusual interest so it is possible to buy for him early and get him exactly what he wants. My mother also has constant likes and a wishlist she updates on a regular basis.
I leave my friends and brothers till later as they are the ones more likely to change their mind.
I don't buy things for the sake of it or because they are on offer. I make a draft Christmas list choosing what I want to buy for each person then spend my time trying to get that item on the best deal possible. Camelcamelcamel is great for that.
I do mention to people I have started shopping and suggest they send me any ideas or update their wishlists so I allow for specific requests in that way.