I don't know what to think about Buzz yet. It has a ton of potential. Combining Yelp, YouTube, Facebook, Twitter, and (considered negative to many) email? That sort of convergence is welcome.
Its current functionality is too bare boned for my liking, and currently the signal-to-noise ratio sucks. I'm scanning stuff multiple times - reader, buzz, facebook, twitter on buzz and twitter linked to buzz. Hopefully Google's going to iterate and tone down the streams, or converge some of the functionality.
The default opt-in contacts visibility is a big mistake. Hopefully the big G's going to Not Be Evil and fix the default to opt-out.
The most common argument against Buzz is "privacy issues!"
The funniest vector for this is Facebook.
It's a Scientologist warning you against cults of personality.
It's a white supremacist complaining about reverse discrimination.
Facebook is the pits for privacy. With Facebook, you should assume any/all information you put up there is not only visible to FACEBOOK, but to any advertiser/person paying Facebook money.
The reason Facebook is free is because we're the product.
Facebook's major privacy problem is that you don't have control over who accesses your data. Anyone on your friends list authorizes a malicious app, and it scrapes YOUR info.
I rate Google as preferable to Facebook in terms of privacy. (I'd rather the bear eat me than the tiger) I've mentioned it before - the internet isn't private.
I think the real problem people are having with Google Buzz is it breaches the demarcation of social network and real life.
Email's more connected to real life, while Facebook is bullshit. Most of the friends we have on FB aren't real friends, they're acquaintances. Our Facebook inbox isn't a real inbox, otherwise nitwits wouldn't spam it so much.
Google's just thrown back the curtain; the life you live on the internet may be hidden by an alias or three - I'm GoingTharn or Dances With Winnebagos or el-ahrairah depending on where you find me in cyberspace. But really, I'm John Barry. That's why I'll never talk about hitting my wife here, or doing heroin at lunch on Fridays, or all the racist rallies* I've been organizing in my free time. That shit's private!
If you don't want it known about you, don't share it. The internet's horrible at keeping secrets.
EDIT: Of course, google's on top of it making this post obsolete as fast as the one I wrote about switching costs.
Also, see? Iteration! This is a very good software design pattern.
* it's not what it sounds like - it's whites-only rally races in the desert.