There is nothing wrong with using the free Web to do research. In fact, for some information (RSS feeds, the content of blogs, the latest news, etc.), the Web is actually the best source for your information needs. There are three things to keep in mind, however, about the free Web:
False Information. Anyone can post content on the Web, making it notorious for the spread of false information. Some websites are just not authoritative (the well-meaning author does not have the credentials to talk about the topic), while others actually deliberately set out to mislead the public or are biased in their view of a particular subject.
The Myth of Universal Knowledge. Contrary to a popular myth, not everything is available on the Web. In fact, the vast majority of materials that students are expected to read and/or study in college are not available on the free Web. A great deal of information is only available via searchable, and often not free, databases.
The Elusive Source. Some free Web-based material is just as good as published material you find in the library, but beware. Much factual information that is on the free Web, while not necessarily incorrect, is far removed from its original source and may be taken out of context. The original source, such as a research study or academic report, offers much more reliable information and should be located whenever possible.
Here are two Web applications that allow you to evaluate a Website's context (how long it has been around, who uses it, etc.)