Recently I've discovered by accident that there is a lot of porn and nudity on youtube.
I've been doing an experiment. I've made a list of keywords that get a lot of porn and nudity in the search results of youtube. A lot of those get through youtubes content filter. In little more than a week I probably flagged more than a thousand video's. It took me a while to notice a patern:

-new users that post porn get their video's removed and get suspended right away
-spammers with followers can upload 100's of video's and don't get suspended for at least a month or two.
-there is a category of explicit video's that only perverts watch so nobody flags these. Examples include wet t-shirt contests(often contains full frontal nudity), t-dj's and certain music video's that contain porn. (Some of these had  many thousands of viewers).
-a lot of porn does not have a descriptive title, a description or keywords. These can only be found via the suggestion bar or playlists.

Please note. I'm not against nudity in a medical or art setting as long as they are age restricted or at least contain a warning(like nsfw). With porn and nudity I mean full frontal nudity and explicit sexual acts, not an exposed butt-crack.

My suggestions for youtube:
-make flagging system where you can not only flag a single video, but also a playlist or the uploader. This is an effective way against spammers and nonlisted video's.
-video's that contain spamlinks in the desciption get flagged automatically(even if they do not contain porn, they at least contain spam)
-use some sort of crc system to detect reuploading of previously removed video's(some users upload the same video 100 times)
-make a black list of banned music video's
-encourage people to flag video's more