The data continues to come in regarding the increased usage of mobile on Cyber Monday: ComScore estimates that roughly 18 percent of online shoppers used a mobile device to access retailers’ sites on Monday, and IBM saw a 70 percent increase in mobile shopping over Cyber Monday 2011.

But Bill Snyder of CIO takes a hard look at how retailers handled that increase in mobile traffic and comes away unimpressed. Shopping on a mobile device was “a wretched experience” Monday, Snyder writes citing a study from Keystone about how mobile retail sites performed. The spike in traffic doubled the load time of the average mobile site, Keystone found, and 5 percent of requested pages never loaded at all.

That’s no surprise to anyone who’s spent much time surfing the web on a smartphone, of course. Many sites still aren’t optimized for the smaller screens and different use cases of mobile, and many of those that are can still be frustrating — if not impossible — to use. Those problems will only increase as mobile sites get more functional by enabling consumers to make purchases, for instance, and compare different products. Retailers can address some of these concerns by building apps for specific platforms, but that solution addresses only a fraction of the overall mobile market. For most retailers, the top priority here should be to building mobile sites that make it easy for consumers to shop and buy — and that can handle the ever-increasing number of consumers shopping on their phones.