Kathy Sierra looked into both formal and conversational style of writing and how does it affects ones learning and retaining the knowledge. She suggested books written in conversational style of writing are more likely to be retained and recalled. There are some studies behind this theory:
… A study from the Journal of Educational Psychology, issue 93 (from 2000), looked at the difference in effectiveness between formal vs. informal style in learning. In their studies, the researchers (Roxana Moreno and Richard Mayer) looked at computer-based education on botany and lightning formation and “compared versions in which the words were in formal style with versions in which the words were in conversational style.”
Their conclusion was:
“In five out of five studies, students who learned with personalized text performed better on subsequent transfer tests than students who learned with formal text. Overall, participants in the personalized group produced between 20 to 46 percent more solutions to transfer problems than the formal group.” …
I would say it is true for some readers, because formal written sentences are harder to understand and digest for some people.
Conversational writing kicks formal writing’s ass – [Creating Passionate Users]