E-mail is one of several insidious aspects of technology. E-mail offers great mobility and efficiency. However, e-mail lacks the authenticity of handwritten and verbal (face to face) communication. E-mail has been described as a perversion of actual handwritten letters and notes. Thus, we'd have to say text messages and tweeting are a perversion of e-mail.
This is going to become a problem because even though most people are tech savvy, they simply don't know how to write. I don't mean composing something meaningful on their laptops or netbooks - although that, too, is fast becoming a problem - I mean that people literally don't know how to write. Legible cursive handwriting is becoming almost non-existent.