"Note that leaving a community will not remove it from your Friends list. To remove a community from your Friends list, see http://www.livejournal.com/support/faqbrowse.bml?faqid=61."
This is no longer necessarily accurate -- an option to remove communities from your friends list when leaving has been added recently. I'd suggest modifying the FAQ to read, in full, as follows:
You may leave any community by simply going to the Community Info page of the community you want to leave and clicking on the "leave the community" link at the top of the page. When doing so, you will also be given the option of removing the community from your Friends list. Please note that if you are trying to remove a community you maintain from another community's Member list, you will first have to log in as the community account itself, then follow the previous instructions.
However, if the community you would like to leave has been deleted or suspended, and you can't view the Community Info page, you can go to the Admin Console (http://www.livejournal.com/admin/console/) and execute the following command:
community <community> remove <user>
Do not enter the < or > symbols; these are only for reference purposes. Replace <community> and <user> with the username of the community and your username, respectively.
As an example, if user gooner wished to remove himself from the lj_userdoc community, the command would be:
community lj_userdoc remove gooner
Note that leaving a community using this method will not remove it from your Friends list. To remove a community from your Friends list, see http://www.livejournal.com/support/faqbrowse.bml?faqid=61.
in short, that is: add a reference to the "remove from friends list" feature in the middle of the first paragraph, and modify the final paragraph to specify that it only refers to the admin console method.