Update: the IWF have now removed the page from the blacklist.
Wikipedia currently presents you with the following message when you try to edit content:
Wikipedia has been added to a Internet Watch Foundation UK website blacklist, and your Internet service provider has decided to block part of your access. Unfortunately, this also makes it impossible for us to differentiate between different users, and block those abusing the site without blocking other innocent people as well.
Wikipedia took this action after the Internet Watch Foundation blacklisted the Virgin Killer album page. As a result Virgin Media, Be/O2/Telefonica, EasyNet/UK Online, PlusNet, Demon and Opal are filtering the page through a transparent proxy, which basically amounts to censorship.