Doing research online does not excuse a researcher from following ethical protocols or filing IRB applications.
Whether you are doing research online or researching online communities you need to think carefully about what you are planning to do. Ethical issues such as informed consent and protection of privacy arise quickley. Is the community public or private? Are you researching persons or avitars? Can documentation of consent be waived? Is there potential of harm to an individual or the community?
Here are some links that may help you develop ethical online research.
Eysenbach, G., & Till, J. (2001). Information in practice: Ethical issues in qualitative research on Internet communities. British Medical, 323, 1103-1105.