Sexually explicit imagery is a problem for Wikimedia in general, and we have had child pornography uploaded to Commons (and presumably other projects) in the past. We can't prevent the upload of underage imagery, but we should do our best. See further discussion at the Village Pump: http://commons.wikimedia.org/wiki/Commons:Village_pump#US_Section_2257_and_W...
We may not be able to meet the legal requirements of that US law, and if we cannot we certainly should have a disclaimer stating that - I've had an attempt at http://commons.wikimedia.org/wiki/User:Nilfanion/2257 At the very least, such a disclaimer helps downstream users of our content avoid legal issues of their own.
Even if we cannot create records satisfactory for legal purposes, we have a moral obligation to confirm as best we can. To that end, it might be beneficial to create a special OTRS queue; we could then have a record asserting that the image is legal. That way we will know to our own satisfaction, which given the nature of many of the penis pics on Commons is a lot better than the status quo.
To avoid fragmentation of the discussion, it is probably best to discuss this on-wiki at the VP.
Thanks,
Nilfanion