If you begin with Andy's post at Older and growing... but first read the history of the various bloggers on this topic,
( via Andy: The current dialogue began here, was picked up here, here, and here, and echoed in a parallel thread here.) ...
... then this is a part of my response. I don't know if I will have time to pick up the thread again, but if the topic continues I will try to keep up.
In its strictest sense one's persona is the outward self we present to the world. It has variously been called a facade of the whole person, a shell of the person- the mask we wear to face the world. Within the persona are the roles we adopt in daily life and the ways we respond to others. At times some people forget that they are neither the role nor only the outward projection they present to others. And there are some reinforcing aspects in our use of different personas in different environments.
I would suggest that there is a need within most if not all of us, to be understood in a full sense without the masks and that there is danger when we ignore the truth of ourselves that these are only pieces and not the whole. I could go on a tangent about the uses of personas and how it can be functional at times to adopt certain roles in and during the moments we need them. But those are thoughts for another time.
I think Andy is right- we must work harder online in a text only world, to reveal the things that others might see in person.
But in working a little harder, we might actually reveal more of our inner selves than perhaps others notice in person.
It is true that there are people, who are completely different in person than online, but I am not sure that doesn't also reveal something secret about the person who is perceived in that manner. For if we are very different online than off, we may be pretending online to be something we wish to be in the rest of our lives or hiding something that we don't wish others in face to face interactions, to see about ourselves or we have some hidden agenda that we don't wish anyone to see. There are likely more reasons and from a psychological perspective, they might be interesting to explore, but that is another tangent.
I have run across "fake" persons online. In some places they are more abundant than in others. We run across "fake" persons in the face to face world too. They are the con artists and manipulators of the world. They are the insecure folks who are very afraid that we won't like them. And they are the ones who want something from us that they know or think we would not willingly give.
In a world of text, the body language, facial expressions, vocal inflections and other mannerisms we use to interpret the spoken word are missing and we feed a bit of our own perceptions into the blank places to compensate. We may use other things to add some context, such as webspace design or links that the person finds interesting or the shape and color of the text they use, even the smiley faces they insert in instant message conversations. We fill in the rest of the blanks with what we think should be there- based entirely on our own perceptions about the face to face world and if we have been around a while, our perceptions of the online world as well.
I don't think this makes online "personas" more likely to be faked any more than face to face personas are faked. I think that makes this just one more place that we use masks to face the world. I think the masks might have as many holes online as off, once you get used to looking for them.