SPAM is bad enough as it is and the last thing we need is to be getting spammed by another ning network. I'm not going to mention any names cough HarleyRadio cough.
If your stooping to the level that you feel the need to spam other Ning networks your pretty pathetic and probably won't have much luck in building a successful network.
Ning should make this a volition of their TOS and terminate networks guilty of this.
Blog talk radio are bad about this also I seen ..coming on sites to recruit people to speak on their talk radio..But I alert them of our policy on site..when you sign up you agree not to spam commercial ventures or ther social sites..basicaly is first warning.. and that we have sponsored members ..we sponsor them they sponsor us..and even pay for ads for magazine..to help support site..we have our interest to look out for also..so if one is on your site basically have no interest in content of your site ..then you already know your interest is not of their concern in first place..and are no benefit to your site..unless some agreement is made to do so..agreeable to both to help each other..