How important is your screen name in online poker?

In fact, chosing your name could matter a little (EV-wise). You can e.g. think for example to set a name that bugs hand history parsers/importers.

Another example is, iPoker and others sites will shrink long names, hence name containing a lot of WWWW-s will be shrink, and not scrapable (even for a human hard to read), hence bug some HUDs and other profiling software. Similarly, mixing up "I" (capital i) with "l" (lower case L) on some sites confuse your username, so people will most often misunderstand it and fail if they want to google you etc.

While it's not a huge deal, it is definitely better not to include modern forum-style slang terms, or riffs on other well known players' handles, in your screen name. For instance, a player called OMG3BetJammerDonk777 clearly has talked about poker with others, and is not nearly as likely to be a passive fish who just took up online poker after years at the kitchen table.

I use every single piece of available information, no matter how seemingly insignificant, to cobble together a picture of the players I'm up against. A player with poker forum slang in their screen name is MUCH more likely to be aggressive, much more likely to have seen a training video, much more likely to understand concepts like hand range, SPR, etc. That doesn't mean they are any good, it just means they are very likely to have certain tendencies.

Put yourself in the position of your opponents when choosing a screen name, and try to pick one that doesn't give them any info about you or your level of experience.

I pay absolutely no attention to what other players screen names are.

Pictures only get my attention if they are unusually attractive or hideously ugly.

While it is not possible to ever intimidate anyone with your screen name, it is certainly possible to irritate other people with it, particularly if you have the option of including a picture with it. For instance, at Bodog I called myself DeathrowJethro with a picture of Wesley Willis, and was called a stupid n***** multiple times. It is hard to believe that anyone who has crossed the line that far is playing optimally.

I have also heard that putting your name in ALL CAPS irritates people greatly as well. Though peoples' reactions and behavior can be difficult to predict, I would think it would be somewhat helpful to be irritating to other players.

One thing that is guaranteed to help you is to change your name regularly at sites that allow this. Although the notes on you stay the same (which allows observant players to still track you), this will definitely punish lazy players who don't take the time do these things. I know this because it has foiled me before when I confused one player's tendencies with another who had recently changed his name be similar to the first player. It probably cost me only about $20, but poker is a game of small edges, no?

I believe screen presence is important so you should put some effort into your screen name and picture.

I dont believe it is that important. Let your play do the talking.