I find wiki very useful as a collation of information on any given article.
However, as people have mentioned, you can not accept anything written as fact without further validation especially with contentious material or disputed information.
I tend to validate the info I need then if it all parses okay, use the specific wiki pages as a convienient source rather than having to construct my own repository. I've found plenty of errors though and had to disregard some entries and edited a few myself to make corrections.
Facts about specific people are the worst and most suciptable to people purposefully changing and posting false information.
Celebrities, politicians etc usually fall foul of these.
Generic info on say Greek Philosophers, Nobel Prize lists or Amazonian insects are usually fine and a great reference starting point which is what I usually look to wiki for. The starting point like a childrens atlas or encyclopedia that gives you the basic guist so if you find something interesting you can research it more fully and accurately elsewhere.
Wiki is in general, considerably more accurate than many sources out there, especially in the media, so whilst keeping an open mind and mild skeptiscism, I would not dismiss it all out of hand due to specific inaccuracies, I sugguest you check how many editions and re edits occur on well know and respected journals, encyclopedias and dictionaries.