The Washington City Paper writes about The Washington Post's 10 Principles for The Post on the Web. They're worth reading.
The most intriguing and difficult ones, I think (oops, there's an opinion):
Accuracy, fairness and transparency are as important online as on the printed page. Post journalism in either medium should meet those standards.
We recognize and support the central role of opinion, personality and reader-generated content on the Web. But reporters and editors should not express personal opinions unless they would be allowed in the newspaper, such as in criticism or columns.
Rich Rubin walked this line beautifully in his Q&A as Dr. Traffic. He maintained his credibility as a reporter by keeping his opinions out of his dialogs with readers online, but he fostered transparency and fairness and a look inside his notebooks with his answers. I hope someone has archived that work to share with others who try the same thing. Rick Thames does a good job with his Q&A online as well, and that format gives some control over the space that a blog doesn't.
Line editors as well should take care in blogging opinion on the web, lest they erode the credibility of their editing. (Oops, another opinion).