If you're thinking of writing about your job in a Weblog, let Mark Jen's mistake be a lesson in what to avoid.

Jen is the 22-year-old blogger whose career at Google was cut short after he went too far in writing about a company sales meeting, his pay package, and other things best left for quiet hallway conversation on, of all places, his "Ninetyninezeros" Weblog. On Jan. 28, only 11 days after he started at Google, Jen was fired.

"It was pretty shocking," he said in a Feb. 15 interview, having had a couple weeks to reflect on what went wrong. "What I didn't know was that the corporate culture at Google was a little more guarded than I had experienced. People weren't blogging about the culture and community at Google. It promoted secrecy as a competitive advantage, and I didn't realize that."

Lesson #1: Know your company's corporate culture before you blog about it. A 2003 graduate from the University of Michigan, where he studied computer engineering, Jen moved first to Seattle to work for Microsoft and then, after 18 months there, to San Francisco to join Google. When he started the Google blog, Jen intended it mainly for his ever-widening network of family and friends, expecting only about 100 people to read it. Within two weeks, however, there were over 200,000 visitors, as other bloggers buzzed about Jen's decision to remove a few sentences of previously posted material. "What specifically did he redact?" people wanted to know. "Did Google make him do it?" In a Jan. 31 cover story titled "The Weblog Question," InformationWeek used Jen's experience as an example of the complexities that can surface when people blog about the workplace. Lesson #2: Blogs may feel like a whispered conversation with a few close friends, but they're more akin to speaking aloud in a crowded public place. According to Jen's account of things, some provided on his blog and some in an interview, he was pulled aside by a manager, who warned him that certain kinds of company information should be avoided, especially anything related to Google's financials. So Jen edited out some of the earlier postings and assumed things would be OK. Within days, however, he was dismissed, without much in the way of explanation. "I look back, and I wonder what happened," he says. "They never gave me a definitive answer as to why." Jen doesn't believe the content he posted violated the nondisclosure agreement he had signed at Google. A Google spokesman declined to comment on Jen's situation. Lesson #3: If you post sensitive content on your blog, it may not be enough to revise or remove it. Content gets cached on the Web. It may already be too late. Jen was hired by Google in January after working at Microsoft, where he started out in software testing and Web services before transitioning over to work on mobile connectivity for Exchange users. He blogged there, too, but his postings tended to be more technical in nature. They were more like work-related communiques than workplace critiques. "I treated that blog pretty much as a technical resource for the community," he says. At Google, Jen signed a standard NDA -- prohibiting public disclosure of trade secrets, inside information, that kind of thing -- but says the company never provided him with a formal policy on blogging. "The key message is, if you're an at-will employee and you want to start a blog, make sure to ask your employer for a policy and what is and isn't accepted," he now advises. "There's definitely a dire need for companies to put together definitive blogging policies." Lesson #4: If your company doesn't provide a blogging policy, ask for one. At a minimum, have an open discussion with your manager and maybe even an HR person before getting started. Jen's now in the job hunt again and says he's wide open about what comes next. Business-strategy consulting, developing emerging technology for another company, graduate school, self employment "- they're all on the table. And, yes, he does plan to continue blogging. "I think it's going to be the next big thing on the Internet," he says. Nevertheless, Jen says he'll ratchet back on the blogging if he finds just the right job at a company that discourages it. "I'll respect that," he says. Lesson #5: When it comes to blogging about work, don't make the same mistake twice.