The SEC and Quiet Periods....
First, my quals: I was on the VA Linux IPO team and had to interact with the SEC while running our friends and family program.
The quiet period is a misnomer. you can talk as much as you like, there is no law against it. A wise company vets its communications with their lawyers who then communicate with the SEC if they have any question as to the nature of the communication.
Eric Schmidt can scream from the rooftops that he think google stock will sell at $300 a share within 2 weeks of release onto the public markets. And if he is wrong , the boys and girls at Milberg Weiss will be waiting. But it isn't against the law per se for him to do so.
So for a google blog, so long as there isn't things in there giving any kind fo stock guidance, or related stuff, they can be pretty safe and allow a certain level of interaction. The reason so many companies clam up is that for many companies they can't count on all of their employees to understand the subtleties of what they can and cannot discuss freely without attracting shareholder lawsuits.
There is a lot more to this issue, but thats the broad strokes. In short: if you want to avoid lawsuits, clam up, or make sure your people understand what it means to communicate with the public markets.