Sayan points us to the official IBM policy on corporate blogging and further to Tim Bray’s reactions.
James Snell describes the construction of the IBM blogging policy:

The core principles — written by IBM bloggers over a period of ten days using an internal wiki — are designed to guide IBMers as they figure out what they’re going to blog about so they don’t end up like certain notable ex-employees of certain notable other companies. They’re also intended to communicate IBM’s position on such practices as astroturfing, covert marketing, and openly goading or berating competitors — specifically, don’t do it. As these guidelines were being drafted, we drew heavily upon our own experiences as bloggers and the excellent prior art in this space graciously provided by Sun, Microsoft, Groove and many others who have drafted policies and guidelines for their employees.

Snell also has a great parody of corporate activity policies on his blog called “Guidelines for IBM Breathers: Executive Summary”. One of my favorites: “Try to add value, and for goodness sakes use a breath mint.”