Wikipedia's good for casually looking things up - if I'm curious about something, that's the first place to go. There is vandalism, astroturfing, articles written to make a particular person, company or organization look good, etc. so things from Wikipedia should be taken with a grain of salt.

If I'm doing more serious research, I'll use Wikipedia to find sources, and then use the sources directly, along with other sources I may find with Google or (gasp) offline in a library. That usually gets me enough accurate, reliable information to get me going.