The study asked people to perform a range of typical tasks from finding information about a bottle of wine to looking up a flight time using their own mobile devices. The firm found the average success rate in completing these tasks on the mobile Internet was 59% compared to 80% for the PC-based Web.

When participants went to sites specifically designed for mobile phones, the results were better: they completed tasks at a 64% rate-much higher than the 53% for using "full" sites, or the same sites that desktop users see.

Not surprisingly, people using higher-end phones with larger screens did better. Those using a touchscreen phone, such as an iPhone, had an average success rate of 75% compared to 55% for other smartphones (with midsize screens and A to Z keypads) and 38% for regular cell phones.

Nielsen advises that services suited to mobile use, like news and social networking, should probably created a dedicated site for regular cell phones as well as a site optimized for more sophisticated phones. Other sites should focus on developing a mobile presence for smartphones and touchscreen phones.

And while loading on complex mobile features isn't a smart strategy, task-specific apps, like those for the iPhone, can help users do variety of things such as finding a nearby store location.

The findings will hardly come as a surprise to mobile consumers, Web publishers and marketers. Because smartphones, especially the iPhone, generate a disproportionate amount of mobile Web and application use, they've captured much of the attention around mobile marketing. That was underscored by the recent IAB mobile conference, where the agenda emphasized advertising and other topics related to smartphones.

Regardless of device type, the Nielsen Norman report stressed the importance of having developing mobile-tailored sites so every user interaction with the mobile Web doesn't end in frustration. That goes for ad landing pages as well. With years to go before mobile connections are as fast as even a modest cable modem, that's the least publishers and advertisers can do to improve the user experience.