True, but there is a great deal of reliable information on wikis. You just should be in the habit of not relying on any single source.
Yup.
I hate when people complain that Wikipedia isn't accurate. No, it's massively accurate and an excellent starting place. It's just not the ending place for anything of importance. It will have errors, biases and smears. So will any book you buy. So will any magazine you read. This is why, if the topic is important, you seek multiple sources.
Conveniently Wikipedia has multiple linked in every article. It's usually pretty important to read these, too, to see if they fully agree with the article, see what the context of the information cited is, and see what information was left out.