The Wikipedia Question
Print encyclopedias (and the online equivalents of the print publications) are excellent sources of general information about a topic. They are not good sources for up to date, complex, or controversial topics. That's not what encyclopedias are supposed to do. They provide a summary of the knowledge about a topic at the time of writing, which may be well over a year before publication. Encyclopedias are a good starting point for research, but in most cases should not be the ending point, especially at the college level.
Wikipedia has some advantages over print encyclopedias, and some disadvantages. Information can be updated by the minute, so out of date information is easily replaced. (The pages on disasters like the London bombings are great examples. The London Bombings page was started minutes after the first reports, and has been updated hundreds of times so far as more information comes out, as rumors are confirmed or proved false, and as more people join in with details.) Because anyone can start a new page (and there are no page limits), topics that normally would be deemed too obscure for a general encyclopedia are included. Print encyclopedias generally find acknowledged experts in the field in question to write the articles, which leads to an authoritative, conventional view that may not reflect cutting edge thinking in the field. Wikipedia invites alternative viewpoints (see Neutral Point of View) so readers can get a more complete picture of the current state of the field.
All of these points are also disadvantages. Since anyone can edit (almost) any page, readers have no way of knowing how authoritative what they are reading may be. Since there are usually plenty of people with good knowledge on the subject watching over any particular page, really bad stuff does get removed. However, the average reader who knows little about the subject doesn't know if the information they are looking at at any particular moment is good. Maybe they arrived just after a prankster.
Using Wikipedia as an authoritative information source takes some skill. The reader needs to learn to check the revision history, to check back to see if editing has occurred, and to check the information in other sources. This is exactly what a researcher should do for any information source--does the information make sense in the context of the rest of the information that the researcher has or finds later? If the National Dictionary of Biography from Oxford University Press can have multiple errors in both fact and interpretation, we need to be careful with any information source. At least Wikipedia has a correction mechanism that doesn't wait for the next edition. (Encarta has recently adopted a feedback policy for users to submit corrections.)
As a librarian and a faculty member, I would not recommend preventing people from using Wikipedia. But I would insist that information found there be confirmed. One of the easiest methods of doing this is to suggest that students use encyclopedias (including Wikipedia) to get started, but that they shouldn't include any encyclopedia in their reference list (or that encyclopedias won't count towards any minimum number of references required.) A more complex, and probably more valuable, lesson would be to ask for a draft or outline using encyclopedias and other general resources, then demanding more specialized sources for the final version of the paper. This helps students learn that some information sources have more value in the academic world than others. It also exposes them to value of general reference resources, such as encyclopedias, when they are starting a new project or need background information on an incidental topic.
It is often very difficult to find information on a topic about which you know little or nothing. Encyclopedias, print or online, fill in that information gap to get you started. But all information, from any source, should be viewed with skepticism in proportion to the value of the information. Confirming a historical date for a side note in an English paper is a good use for an encyclopedia, including Wikipedia. Resting a historical thesis on the date given in Wikipedia, or any single source, is risky scholarship.