I thought this was old hat, even when I was in school we were also told not to use Wikipedia as a source since nearly anyone can edit it and their credentials could be suspect, therefore the information could be as well.
Some areas have gotten a lot more scrutiny and are better than they used to be but are still bad (ex history and politics as others mentioned).
Science stuff on there is still rather superficial and over-simplifies a whole lot (issue that was there say 10yrs ago), but its a lot more branched out than it used to be.
For internet doomsday scenarios wikipedia is a nice rough reference rather than a definitive guide, it was never meant for the latter as an encyclopedia. It'd be a poor call to teach off it alone vs dedicated websites or various textbooks and so on.