Pew / Internet (PDF):

Most teenagers spend a considerable amount of their life composing texts, but they do not think that a lot of the material they create electronically is real writing. The act of exchanging emails, instant messages, texts, and social network posts is communication that carries the same weight to teens as phone calls and between-class hallway greetings…. Yet despite the nearly ubiquitous use of these tools by teens, they see an important distinction between the “writing” they do for school and outside of school for personal reasons, and the “communication” they enjoy via instant messaging, phone text messaging, email and social networking sites.