I love using Wikipedia. It is my first port of call as far as any type of encyclopaedia is concerned. The content is up to date and has been proven to be, almost overwhelmingly, reliable.
Wikipedia is more than an online encyclopaedia though. Just as I discovered Google is more than a search engine through my journey into Google Apps, Gmail, Voice and so much more. I found out about Google providing a vast range of resources and tools by clicking on the 'more' link on the home page a few years ago. Since then I haven't looked back and have become one of Google's biggest fans.
I believe that the same can be said for Wikipedia. Scroll to the bottom of the Wikipedia home page and you will find the likes of Wikiversity, Wiktionary and Wikibooks, just to name a few. My personal favourite is Wikiversity. Take a few minutes to have a look. Beware though, you may find the the few minutes you planned to spend browsing will turn into a few hours.