The popularity of photo-chat app Snapchat has many interesting aspects. One I find particularly interesting is that Snapchat has a very poor memory to be a messaging app. It remembers who sent you a photo or video message, but the message itself self-destructs within 10 seconds.
The lack of memory creates a different social space and different behavior. Maybe it turns out that forgetfulness as a design principle mainly increase sexting, but my guess is that many other uses will be driven as well when the system self-destruct messages instead of saving them forever.