As far as I can tell, it is filling a tab on my inbox with random messages from people I've never heard of (though presumably are in my email address book or something), saying things like "I am testing Buzz."
How is this supposed to improve my life?
Improve your life? I don't think anyone can answer that yet - it depends how people end up using it. And if you decide you don't like it, opt out.
Disabling Buzz: http://news.cnet.com/8301-17939_109-10451703-2.html
They're marked "Twitter - Public" instead of "Buzz - Public", which is probably the reason they're un-unfollowable. Unfortunately, they're also the loudest and most innane of the bunch.