As Author Cheryl said, it's not to be trifled with because it's against the law in a lot of countries. The sad part is that while there is a lot of action to take on it (in the UK, police do not rest until cyber bullies have been apprehended and that doesn't take long), it's not viewed that seriously because it's not nearly as visible as physical bullying. You will notice depression in someone who is cyber bullied and even the scars of physical self harm, but you can't find evidence of someone doing it to the reciever unless you check their phone, computer, etc.
I find that a lot of (but not all) people who get involved in cyber bullied manage to do it themselves. There's a lot of security features on social networking sites - a common source for cyber bullying - that prevent others seeing personal information or using things against the victim. As the saying goes, "there's no smoke without fire", but it's a shame that's not always the case.