From what I have seen so far, I like Google Buzz. It is still pretty unpolished but it could become a real competitor for real-time streams and even company collaboration tools.
One thing I don’t like and what I think must change immediately is the option to edit your post. It comes in handy to fix a typo but it can very well be misused. Check out this real life example to see what I mean.
Here is the corresponding comic: