Here’s a study by Jakob Nielson:

http://www.useit.com/alertbox/mobile-usability.html

This study is over a year old, but I think there are a few takeaways.  One is that the success rate of people with “touch” phones is 75%, which is pretty high.  Given that smartphones seem to be going more toward the touch screens, this bodes well for regular websites.  The other is that mobile users are highly “search” reliant – so search engine optimization efforts will continue to matter quite a bit.