Google Buzz: bzzt!
A third decision was unambiguously (IMO) bad: they made it opt-out instead of opt-in. I am having trouble thinking of a single case where it would be a good idea to automatically, and without notification, make changes to existing accounts. [Edit: I meant good for the customer, and not counting things like "hey, we gave you more disk space". I mean new behaviors.] Auto-on for new accounts is quite defensible (with documentation); changing the behavior of accounts that people set up on the basis of a different implicit contract, no. Especially if you haven't previously sent out an update to your privacy policy.
There's one more problem with Buzz: opt-out doesn't really work. If you do the obvious thing and click on the "turn Buzz off" link, all that does is remove a shortcut. Your connections are still there. That's just bad engineering.
Google says they have heard the feedback and will fix things in a few days. And, while I can't verify this without a second account, some people believe that deleting your profile keeps Buzz at bay. [Edit: confirmed with the help of another gmail user, thanks.]
Buzz could, potentially, be a useful tool, though it remains to be seen whether the world really needed yet another attempt at a social-networking site. But their roll-out of it has left a bad taste in my mouth, so I'm likely to wait a while, until I hear positive reviews from people whose opinions I value, before I touch it. And I'll have to be certain that they aren't publishing information that (otherwise) exists only in my mailbox. Linking to my public Picasa album is fine; it's public (same as the vast majority of this journal). Telling the world who I correspond with and how often, however, is not.

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There's even a position between opt-in and opt-out that's likely to benefit companies: "we'll sign you up in a week if you take no action". Think of this as the book-club model where you have to send back the reply card to not get the selection.
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Sadly, that's not silly, but appropriate. When(/if) companies discover that it will be incredible.
There used to be cases where it was nice, back in pre-internet days: you buy lots of games from this catalog, maybe you get mailings from some other catalog they opted you into. I found that to be very cool, because they were targetted and I had no idea those companies existed. In these days I think it is more an annoyance than a service.
The bool-club model.. I don't like it personally because I procrastinate and get burned. But that's my fault, and you're right, it's a balance. "We'll spam you this once but click on this link and we'll remove you from our database and not send your email to any other company" would be acceptable.