I would leave it off entirely. Law school deans, etc (I'm a 2L myself) view this stuff different than you or I do. I had a buddy in undergrad kinda like you- he made a KILLING playing online poker. Frankly I told him he couldn't NOT do it. And some of these people you'll be interviewing with will understand it but a lot of them won't since it's a more or less recent phenomenon. When I dabbled for a while- my parents thought it was stupid, waste of time, juvenile, etc even though I was doing pretty okay. It's risky putting it on there because here's how it could come across (right or wrong, perception is everything): Had a job, you quit a job to gamble (albeit "professionally" or whatever label you want to put on it), meaning to take big risks, which is even more reinforced by the fact you weren't doing both at the same time but quit your steady job to take the risky one. They would argue you lack stability.
Personally I would leave it off entirely. You put "self employed" or something they're really going to want to know about that because that sounds like something really innovative and interesting. They're envisioning you working out of your garage or starting your own side business or something and then when you say "I played online poker" they're going to go "oh."
Especially in today's market, an 8 month gap in employment is NOT that big a deal and probably fairly common. They may not even notice it. If they really press you about what you did during that time just say you held a series of odd jobs to get by. You're not lying. And if they push you more on it then tell the truth but caveat it with "I left it off because I know how it could be perceived" etc and just tell your story as you normally would. You don't have to be ashamed of it or anything, I just think it's risky to advertise when a lot of people don't understand it and gives people wrong impressions.
That's my biggest fear. Once I say it, I can't "unsay it." And, somebody from an older, more conservative generation might see it and turn their nose up at it.
However, I've been leaning the opposite direction for a few reasons:
1. If they see an 18-20 month gap (March 1, 2009-November 16, 2010 I think), I'm worried they will draw their own negative conclusions. If it were just 6-8 months, I think that would be more easily shaken off as part of the job market being down.
2. I didn't do well in undergrad, primarily for two reasons: poker and partying. My priorities were way out of whack. A big part of my personal statement (which is only a rough draft right now) talks about how I've matured since college and have "re-focused" on what I originally intended to do. But, it's hard to explain my bad GPA without mentioning poker unless I lie, which opens a whole new can of worms that makes me nervous. I could just skate around the issue, but I would think a more genuine, sincere statement would have a better impact. At the same time, if they see bad grades (prob 2.7ish) AND an extended period in a "taboo" industry they might not care what I have to say.