It used to be that getting written information out to the masses was an involved and formal process. Your options generally included that you could write for a newspaper or magazine or you could write a book. You had to be knowledgeable of what you were writing, and very often, you had people reviewing your work, and frequently, you had to site sources to prove what you were saying was true. Then, if you wrote something that wasn't accurate, or plain out wasn't true, someone would come under fire, and you could even possibly lose your job.
Now, with the ease of online publishing, you are able to put information online in seconds, and the risk associated with publishing inaccurate information is basically nil. Consider that you can put up a free web site in less than an hour, you can post a blog article in minutes, and you post a message to a discussion board in seconds. And the fact of the matter is that you can write about virtually anything, and there will be some out there who will believe it because it was online.
So the question is, when you're reading something online, either on a web site, in a newsletter, or in an email that was forwarded to you, how can you determine the appropriate level of trust in accepting that information as true.
First, consider the source. Are you reading a scientific article on Discovery News who is known for their scientific articles? If so, you may want to grant a fairly high level of trust. Perhaps you're reading an article written by someone who presents a long list of credentials on a site that you don't recognize. In this case, you might want to do a little searching on that person, their credentials, and on the article itself. Search for inbound links to the page. Are there a lot of other sites linking here? If so, under what context? Or, are you reading an email message that was forwarded to you, originally written by an unknown or unverified source?
The different methods for researching the validity of an article online vary both in time and value. You can search Google for inbound links. This is quick, but might be low in its value. Writing to known experts in the field is more time consuming, but might have a higher value. Researching the topic online to see who else has written about it can be time consuming as you will probably want to evaluate the reliability of these articles as well. Sometimes, articles will get copied over and over online. Some people try to build sites that attract visitors simply by replicating content they've found online. Are all references to this topic simply copies of this article?
The point is that too many people will read something online and then take it as fact. They'll even pass that information along as if it were true, further propagating the misinformation.
You have to choose. How important is it to you that the information you're reading is true? Are you planning to use that information, or is it just a point of interest. Are you going to let it influence your actions - perhaps in an election, or are you planning on passing that information along to others.
Take into consideration how you plan to use the information, how it will affect you and others if it's wrong, and also consider the level of effort required in verifying the information. After finding the balance, you can make an informed decision as to where your level of comfort is in accepting the written word as truth.