anonymous identifiable
this is a modern one that's more relevant to the internet than the others
lots of noise has been made about anonymity being the bane of the internet (for instance, see this article), but I'm just not buying it -- my opinion is that the people who use anonymity to be rude or nasty or whatever are simply like kids looking for attention -- if these folks are soundly ignored they usually go away
more importantly though, there are good reasons why i want everyone to have the ability to be anonymous at any time -- one of the subtler points is that total anonymity means that even more weight is put on the content being delivered (if you don't know the gender, race, age, geographic location, or physical appearance of the person who's communicating with you, it prevents you from prejudging on any of those bases) -- i just don't understand the arguments of people who calim that they're not capable of conducting a dialogue with someone who won't reveal their true identity -- certainly at the end of the day one can decide to trust an anonymous stranger less than someone who's identity you can apparently identify (not as easy as it looks without mastering some cryptographic tools/concepts in any case, but that's another can of worms...) -- but I think it's folly to make everyone pony up
certainly anonymous trolls are not easy to ignore -- but the point here may be to just work at teaching groups to "collectively" ignore those who would choose to rudely distract (a tough task, as the troll only has to get enough under a single skin with every post in order to keep the dialogue going -- and in a large group or forum, there's usually at least a small group incapable of refraining from feeding the troll(s))