Okay, back again with what little, probably unhelpful info I can share. Sorry it's taken me so long

I was cyber-bullied for months on end in the last two years of high school. 'Cyber-bullying', as it's now known, has been around for much, much longer than Facebook, MySpace, Twitter, and kids having mobile phones. I copped most of it through MSN, which teenagers (and probably you guys) are still using.

I know what I have to say probably isn't terribly helpful, but in a way, kids are kind of gluttons for punishment. It is SO easy to get rid of bullies who are targeting you online - there are so many tools to block, delete, and prevent the bullies' taunts from reaching you.
BUT - and this was my biggest problem - teenagers (and I'm sure we all still feel this way to some degree, adults are just better-equipped to handle it) have this inherent *need* be 'in the loop', and to know first-hand who is saying what about them. So the chances are that if someone is saying horrible things to your child on the internet, your child is not only letting the messages keep arriving in their inbox, but they actually *welcome* the taunts (by not blocking the bully) because they just can't stand to think that someone is saying things behind their back - they want it all out in the open so they can read/hear it, and if not respond or defend themselves, then they are at least not being left out of the gossip and b****ing and know exactly what is being said about them. Being a teen, the worst thing you can imagine is not that someone hates you and is saying it out loud, it's the thought that you remain in the dark about it and everybody else knows, and is laughing behind your back about it.

As a parent, you can do some things to stop cyber-bullying, but in reality, not that much. Programs that allow parents to monitor their child's web travels are a good start, but those things don't stop the bullies' messages getting through - you just get to read it after the fact, kwim? I definitely agree with not letting your child have unsupervised internet access (ie, keep computers in family areas and have boundaries as to what they can and cannot do online), and I believe MSN (which is a major cyber-bullying tool because it's like a chatroom, rather than email or commenting someone's MySpace page) has a function that allows a user to log all conversations, so again, you can see what conversations your child has participated in, but again, it's all after the fact rather than a preventative measure.
These tools work only in that they can help build a case of sorts against a perpetrator - your child *has* been bullied, yes, nobody can take that back, but at least if you are intending on pursuing legal action or even taking printouts of emails, MSN convos etc to the school principal to prove what is going on, you can use them to your advantage.

As far as preventing or getting on top of cyber-bullying before it becomes so bad that a vulnerable child is at risk of taking drastic action, the best thing you can do as a parent is try and take off the 'mum' hat, or at least monitor your child's relationships offline as well as online. Cyber-bullying tends to be just the same as offline bullying, but the inhibitions of face-to-face interaction are removed, kwim? Back in the day, you knew people were saying things behind your back, but you only got whispers, because the bully was too much of a coward to say it to your face. Now, the bully can be safe in their bedroom and saying awful things to your 'online' face without fear of retribution - that's why it seems worse now than it did a decade or two ago.

I found a lot of bullying was from people who used to be friends - this is where I ask parents to be careful. Your son or daughter may never be bullied by anybody, until they break up with a boy/girlfriend or have a falling out with a friend over a boy/girl or another friend, and then the friend/ex/ex's friends/whoever turns nasty. The danger there is that these people, because they were once friends with their target, have a lot of access to the target - they used to text each other after school, now instead of 'goin 2 c movie dis wkend?' it's 'Ur a skank n we all h8 ur gutz'. They are on each others' friends lists on social networking sites, so status updates go from, 'can't w8 4 skewl hols, 1 wk 2 go!' to '*insert name* is a fkn loser, wish she waz dead'. In that instance, it's the equivalent of saying something behind your back - the bully is putting the message out there knowing that the target is going to read it and be hurt, but it's not telling them directly, kwim?
The worst part is that teenagers are pack animals - so if your child finds themselves being ostracised by one person, there is the risk that the rest of their peer group will also turn their back on your child because the other person is deemed higher on the food chain, or that they have more to gain by pledging their allegiance to the other person. And then instead of being bullied by one child, your child could well start copping it from all angles, even those they previously thought were trusted friends who could be relied on to protect them and help them feel safe.
That's when a child becomes a risk of suicide - one bully you can handle. Ten of them, and them being people you were so close to and trusted, is more than a fragile teenager can bear.

If you're worried about your child being a victim of cyber-bullying, PLEASE just reassure them that you don't have to wear the 'parent' hat all the time, and that they can come to you with ANY concern they have. Encourage them to discuss all the lame day-to-day banalities of teen interactions - find out who's dating who, who hangs out with who, who is friends with who and how your child fits into the bigger picture, as this will go some way towards helping you understand if your child does become a target of internet bullies. It's the face-to-face interactions that are important here - cyber-bullies are not faceless, nameless and anonymous strangers targeting your child. Cyber-bullies are usually the kids you previously welcomed into your home as friends of your child.
Educating your child on the power of their words, especially when written and sent via email/text/on social networking sites, can also help your kids to not become cyber-bullies themselves. A lot of teens just don't realise that gossiping amongst themselves on MSN etc can be construed as cyber-bullying, and most kids who taunt others online would not identify themselves as cyber-bullies - just a kid who perceives their target as having 'done something wrong' and 'getting their own back'.