I don’t think they are having the effect they claim to be seeking. I will stare at beautiful naked people, because they are beautiful naked people. However, they won’t convince me to give up eating meat. They won’t increase or decrease my outrage at misogyny in Islamic countries. I am now slightly more aware of issues related to democratic reform (or lack thereof) in Ukraine, so I guess they have had some effect on me.
Still, I like looking at beautiful naked women, so if Peta, Femen and others want to carry on with naked carrying on, more power to them. Just so long as they don’t expect that the awareness (or whatever else) they raise is necessarily related to their target subject!