We strive to make Wikipedia as accurate and as good as possible. If you see something you know is wrong, be bold and fix it. If you see something that seems wrong, leave a note on the article talk page and remove questionable assertions if no supporting evidence is provided. You can also use a verification template to add a citation needed tag after the text in question.
Peer review for accuracy and quality happens constantly through the Recent changes page and watchlists. A review can also be solicited on Wikipedia:Peer review, Wikipedia:Article assessment, and Wikipedia:Good article nominations. If you believe an article is really good, nominate it at Wikipedia:Featured article candidates. More sophisticated approval mechanisms are under constant discussion. Regardless, we do not guarantee accuracy and have a variety of other disclaimers. These are linked from every page, so please do not add more disclaimers to articles!
There is a semi-automated peer review available. The easiest way to install the script is to enable it as a Gadget: go to your user Preferences and check off the MoreMenu, adds Page and User dropdown menus to the toolbar... entry under Appearance and hit save. Each article page will then have a Page and User pull down menu near the top; go to the article; hover on Page; hover on Tools; click on Peer reviewer.