I must say, it's really never too early for me. I am one that truly enjoys Christmas in July also.
I know many people don't like it, and some are just appalled by it, but I think its worth noting that this is retail. Many people's lives rely on Christmas season spending. Whether a person likes it or not, other's need these sales during this time of year to make a living.
I don't really know if having Christmas decorations on display improves sales, but I would imagine it does or they wouldn't do it.
Like others noted, I have seen decorations up already for weeks now at Costco, Michaels, Target, etc.