I have read a number of different opinion articles on the existence of 40k meta-game and its importance in the whole of the game. From a personal perspective, I didn't necessarily believe Meta-game was important. I just figured: "Bring a balanced list, and things will be ok." Then, I started playing at Arkham Games, and my thoughts changed.
After having run a few tournaments at Arkham, I have found some very interesting things about the Arkham Meta-game. For one, there are very few imperial players. There are certainly a few to be found, but they did not place very high compared to the Xenos players. The past tournament had 3 Dark Eldar players, which made up almost a third of the participants. There were also 2 Necron players present, which made half of the whole tournament Xenos. Knowing these sort of facts really does create a specific gaming meta for 40k.
Logically, from the local meta-games and their unique qualities, there must be a national meta-game. With the prevalence of the internet, blogs, and forums, people can easily communicate ideas about lists and list building. It seems unlikely that there isn't a national concept of winning codexes, lists, units, etc.
So, if you come up to play at Arkham, be ready to see Dark Eldar and Necrons all over the place! :P