http://steve-yegge.blogspot.com/2006/09/good-agile-bad-agile_27.html
Google is an exceptionally disciplined company, from a software-engineering perspective. They take things like unit testing, design documents and code reviews more seriously than any other company I've even heard about. They work hard to keep their house in order at all times, and there are strict rules and guidelines in place that prevent engineers and teams from doing things their own way. The result: the whole code base looks the same, so switching teams and sharing code are both far easier than they are at other places.
If you're in the habit of pre-announcing your software, then the general public usually wants a timeframe, which implies a date. This is, I think, one of the reasons Google tends not to pre-announce. They really do understand that you can't rush good cooking, you can't rush babies out, and you can't rush software development.
The difference is that Google isn't foolish enough or presumptuous enough to claim to know how long stuff should take. So the only company-wide dates I'm ever aware of are the ends of each quarter, because everyone's scrambling to get on that big launch screen and get the applause and gifts and bonuses and team trips and all the other good that comes of launching things with big impact at Google.
