If someone adds me to their favourite images or artists list, I usually send a PM and thank them, and ask them what about that partifcular piece or about my images in general that they like. I go onto explain that knowing what people like and dislike helps me improve as an artist.

Sometimes I hear back from the person, other times I don't.

However, just because someone has placed me in their favourites without commenting on any of my images doesn't mean I assume that they are adding me to steal my gallery, or any of the artists that they have in their favourites...and some lists are long....numerous pages of favourite artists.

Speaking from the perspective of just being a Renderosity member, I don't think I would like to be able to remove myself from other people's favourites. To me that is censoring and pretty much deciding for them what they like or don't like. 

I would think that the solution lies in some other way. Perhaps doing something like 3D Gladiator and some other sites do which requires to member to participate before being allowed access to certain features on the site. Or a certain length of time that they have to be either a member or an active member before being allowed to save favourite images or artists.

I've seen some people suggest in other threads about blocking "right clicking" and saving. There are ways around that. Any screen capture program or your "print screen" key on your keyboard allows you to get around that.  As does using some browsers and just saving the web page to your hard drive. If someone wants to steal your art, there really isn't anything you can do about it when it comes to the internet. It's just the nature of the medium.

I personally don't upload anything to the net that I'm not prepared to accidently find one day on someone else's website. 

I know people don't like to hear "if you don't want it taken, then don't upload it to the internet".  While we may not like that type of mentality, it's really the truth.

The invention of the internet opened up Pandora's Box and there is no containing it. The internet stetches far and wide into the most obscure parts of our world and laws are different all over.  None of us have the  time or resources to go around tracking down each violator and suing them.  Besides, the internet is a gigantic "place" and there is no way for you to be able to find all of the hundreds of sites on the net that may have your art on it. 

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi