Wikipedia and its place
Personally, Wikipedia is one of my most used resources. For random curiosity, there's no better way to get a quick overview of a subject or to find an obscure trivia fact. From the history of demolition derbies to in-depth discussion of moon craters to the philosophy of Immanuel Kant, there is something on Wikipedia to get you started. Like Liz described it, it is a great hub.
Detractors will say wikipedia is suspect because anyone can write things, but the real power of wikipedia is that anyone can correct it. If someone complains about something being wrong on wikipedia, it is entirely within their power to fix it. You can't do that with Encyclopedia Britanica.
A few years ago, the biggest problem I found with wikipedia wasn't incorrect facts, but totally irrelevant facts. It seemed that every article (from demolition derbies to Immanuel Kant) would have a "trivia" section that listed every single episode of the Simpsons and Family Guy that the referenced the topic. In the past few years, though, they've really made an effort to clean up these sections. They either have gotten rid of these trivia lists all together, or posted a warning on the page that trivia sections are not encouraged and that relevant facts should be incorporated into the body of the article. The great thing about wikipedia is that it is always improving.
But all that being said, I understand why schools would "ban" wikipedia, even if I don't think that is necessary. I know I wouldn't accept it as a reference if I was a teacher. For one thing, because of its ever-changing nature, there is no gurantee that the fact or quote cited would still be there later for verification (except buried in the page history tab.) As good and wikipedia is, there is surely a better reference out there for any topic. It may be fantasitc for something about everything, but not for any one thing.
In high school we all learned about different reference tools--things like when a dictionary is best, when an encyclopedia is best, or when a magazine article or book is best for a particular situation. Wikipedia and tools like it should just be added to the discussion. It's just another tool with its own set of benefits and limits.
And all of its benefits definitely earn it a place in a school library. Even if it is not good for formal papers, it is fantastic for curiosity, and students should be encouraged to indulge curiosity.
