I like wikipedia overall.
That said, people who don't have knowledge on a subject and run straight to it are the ones it does the most damage to. People like that who don't have enough knowledge on a subject, or enough interest in said subject to further educate themselves after that are the types most likely to read a wiki page on something, assume most or all of it is true, remember those "facts" and never bother reading further or learning anything else about it. I also think it used to be more useful than it is now. On the one hand there is much more there now than there used to be. On the other hand that also means there is more incorrect information there. Not to mention there are types there now that engage in edit wars, revert everything, etc. Just about any subject that can have a slant, or be biased to one side or another, will tend to be. People will sometimes revert edits that merely fixed obviously incorrect information (I mean obvious vandalism) for no good reason, even after leaving the vandalism for ages. Pages that aren't of interest to most can go the longest without being fixed. Some subjects seems to have "experts" there in charge of watching certain things, and sometimes those "experts" are the ones with a clear bias.
I think it is a great idea, but like most great ideas it runs into problems the second people get involved. But yeah, as long as you know not to blindly trust anything you find their, and don't use it as your only resource, it is great.