The idea of creating false aliases is not new but the Internet takes it to a whole other level.  A person could fake being someone else, for years, and nobody would be the wiser unless they are incredibly internet savvy.   However, this may not be as terrible as it might seem, under the right circumstances.

Although I don't believe I need to say it, it is of course forbidden to gossip, spread lies, and defame people.  The laws of Lashon HaRa (evil speech) are extensive and make a person really think about what it is they say and its potential impact.  Hiding behind an alias just makes it worse because it means you have no backbone to stand behind your word.  I don't feel I need to state more on this.

Now the case you refer to was an academic who kept a false identity the reason of self promotion.  This individual used two separate identities not only to "talk themselves up" but also to invent sources that didn't exist and give them legitimacy through a third party.  Such deception is considered to be genevat da'at, the theft of thought.  People were deceived into thinking this person was more widely received and important than he actually was and he was given certain considerations as a result.  Needless to say those considerations have disappeared and he has lost respect in the eyes of his peers, though I'm not sure if he actually ended up losing his job at the end of the day.

There is an idea in Judaism that you should always cite the words of another if you use them.  However, there doesn't seem to be any mitzvah to cite oneself as the source.  Several medieval Jewish works were written anonymously and are still widely accepted.  The Orochat Tzaddik is a very well regarded ethical work and the Kol Bo is used extensively in Ashkenazi Jewish law but the names of the authors are not known.  The Besamim Rosh is actually a medieval commentary on the Talmud that the author tried to pass off as the work of the famed Rosh but became popular in its own right, and was not rejected because the author didn't identify himself.

Truth be told, some books in the Bible themselves are anonymous works.  While we have traditions for who the authors are, in a number of works the authors never identify themselves.  In the case of the book of Iyov (Job), there are no contextual clues about who wrote it at all.  That doesn't affect its universal acceptance by the Jewish people.

So while honesty is quite important, sometimes the message itself is what matters and the name is a secondary issue, and of course there is much more to say on this issue as it is quite complex.

Anonymity is not a crime nor is preserving one’s anonynimity unethical.  However lying, or deceiving (of course) is a problem in Jewish ethics.  So context becomes very important.  If the site on which you want to post is predicated on proclaiming your identity so that others can know who you are, then presenting a false identity is in fact deception.  If the site, or culture of the site, implies no requirement for identifiying oneself in order to comment, simply using an e-mail address that does not identify you in a meaningful way as your name would seem to me to be acceptable.  The e-mail address is real and therefore you have not lied or deceived but you have maintained your anonymity.  I think part of the calculus has to be an assessment of your reason for being anonymous.  If it is to deceive, as in the professor praising himself using an unidentifying (or purely false) identity, then of course it is unethical.  If it is to preserve one's privacy or to be able to give feedback honeslty so that there is no personal backlash, in a forum which allows for anonymous feedback, then I think it is OK.  And to avoid untruth, best to use the unidentifying email address as one’s name when preserving one’s privacy then a fake name, which would be by definition presenting a falsehood.