What's in a name?
That which we call a rose
By any other name
Would smell as sweet.
How important is an online nickname? Each of us have chosen some word, phrase, or series of characters with which to represent ourself, but how much significance do these carry? To some people a nickname may be unimportant, but to others a nickname is an important commodity, and a crises occurs when a preferred nick is already in use.
I have not been using e2 for long, so I don't have much insight to the situation here, however, in general people try to choose a nick for themself that avoids conflict. Something uncommon to ensure that it will be available whenever desired. For instance, I used to go under the nickname Seldon but because it was so frequently taken I decided to switch nicknames to Andukar which has always been free for me.
Not only is it convenient to have the same nickname for AIM, ICQ, IRC, etc... but it also lets people who know you recognize you wherever you are. People attach opinions and character traits to a nickname. In the online world, I have heard of many situations where a person who was heavily disliked as one nickname changed their nick to start over and became popular and well-liked under a new identity. There have also been many situations in which someone has impersonated another person by using their nickname in attempts to slander a good name or to gain access to information / resources.
Fights over doubled up nicknames can range from mild, where one person simply gives up, to extreme, when both people have a strong endearment to their nickname. On IRC it is not unknown for a person to be troubled with DOS attacks from a vicious party who wants to remove that person from IRC in order to get his or her nickname back. We're not talking about play here, we're talking about highly illegal activities. And for what? A nickname. This alone should confirm the significance of a nickname in the minds of any doubters.
Think about why you chose your nickname. Odds are that you've told this story to people before. Odds are you've been asked before. Odds are you're proud of the nickname you use. And you have a right to be. In many ways, it is you.