Jakob Nielsen has summarised the key points from his report on the topic. The main point being that the medium is far less forgiving than the desktop-designed website. Content must be even more concise, IA and functionality stripped back and simplified to only what is absolutely essential.
In a related article by Gerry McGoven, he comments on Nielsen's research and makes a really good (and regularly overlooked) point:
"Web strategy is far more about psychology than technology, blogs, Twitter or any other forms of content. The more people use the Web to live their lives and do their jobs, the more web professionals need to invest in understanding human behavior."
Mobile UX Sharpens Usability Guidelines - article by Jakob Nielsen
You don't need a mobile strategy - article by Gerry McGovern