Yesterday I reported on new data illustrating the need to optimize email messages for mobile. Today a new report highlights the need to optimize websites for mobile users, too.

Keynote Systems' Mobile Retail Index World Editionranks global m-commerce sites based on key performance indicators such as load time and success rates. The latest index shows that British retailers are leading the way in m-commerce.

Marks & Spencer is the number one ranking retailer with a load time of almost half that of the average - 4.86 seconds versus an average 9.55 seconds. The department store also registered a 100% success rate (average 92.72%).

In third place globally is supermarket Tesco with a 5.88 second load time and another 100% success rate.

Mobile platform company Usablenet powers the above British retailers plus many more in US. The firm released mobile retail figures from across the pond in the US earlier this week. Their data shows that mobile traffic to many of the retailers they manage, including REI and JCPenney, was heavier on Thanksgiving Day than on Black Friday.

Mobile traffic was found to be up 160% from the same period in 2010.

Why? Because, says the mobile platform firm, people were spending the day seeking out deals ahead of visiting stores on Black Friday.