Oh hey, people are talking about me...
Yes, I did put SDN on my AMCAS. Yes, it did come up in interviews. No, I don't regret doing it. But yeah, my time on SDN is spent quite differently than most of yours...
I found/find this website to be extremely useful, and that's why I'm still around. I've put a lot of work into the site, and I felt that was something that reflected well on me.
The long and short of it is... every adcom is going to know what SDN is. And yes, it does have a reputation for being a bit high strung and full of crazies. But the adcoms knew who I was on the site, could see that I wasn't one of said crazies, etc. At the time of my application, most of my SDN time was spent in revamping the MCAT forum as I took it over from the previous lead mod of that forum. I lead review sessions via SDN chat, helped with MCAT strategies, rewrote a lot of the stickied threads there, etc. I also organized all the application threads the year I applied as well.
I felt that if a school couldn't appreciate that, then I didn't want to be there. In fact, the dean of admissions at my school continually thanks me for all the questions I answer about WashU on SDN and for being so willing to be available to the applicants and incoming students.
The schools don't hate SDN. The only way SDN will reflect badly on you is if you say stupid stuff, troll, be a huge douche, say bad things about interviewers, complain about the schools, etc. Being invested in knowing what you can about the medical school application process isn't a bad thing. Being a crazy is.
I know people think I'm a bit ridiculous for mentioning it on my application but I'm not ashamed of my affiliation with this site. I did spend a lot of time improving the site so it was meaningful enough to me. And frankly I don't really care if people think it was a bad decision. Because hey, I'm go to a great med school. It obvi didn't screw me over as much as people thought it might.
Edit: Also, I am of the opinion that the professionalism of at least the PA forum has deteriorated over the past two years. The annoying pictures posts are just that: annoying. Not useful at all. Not sure what really happened. We didn't really change our moderation policies to be more lenient. People just seem to get a kick out of being completely useless now or something.