I think language change (in our lifetime) has several influencing factors:
- Laziness/hurried speech. EXAMPLE: the dropping of "-ing" and simply "sayin' I'm runnin' to the store to get somethin'."
- Pop-culture, and more specifically, the hip-hop culture. EXAMPLE: "For shizzle my nizzle." Add this to factor #1 and you get "For shiz my niz."
- Technology. EXAMPLE: brb; lol; g2g. People aren't just typing these things anymore. Initials for common phrases are now handwritten into class assignments (and often formal essays done in class) and even spoken aloud.
- Hollywood. I think it is overlooked as the biggest cultural influence (and certainly technology has only aided rather than competed with it) of our time. Who's saying what (or tweeting as the case may be) in Hollywood somehow makes it into mainstream language the fastest. This is also probably the biggest international language factor as other countries become "Americanized" largely through what they see in the movies.