For me, the main reason I log into this site so often is for the chat feature.
Also, the ability to earn prizes with your activity (chatting doesn't give you XPer btw) is also a pivotal reason why people stay on for so long.
I'm not using the chat recently cauz I'm having computer problems at the moment (my hard drive may be dead in my desktop), and the chat doesn't work on this site when you log in using mobile devices (anything besides a desktop or laptop computer).
But I must say that being on this site for overall 2.5 years now, the majority of users log in regularly to chat and to earn prizes with their XPer points! 8-)
This site is filled with bullsh*t questions and I have deleted my account here many times but then I open it out of curiosity and find a lot of questions I just HAVE to answer and... f*** it - I make a new account again!
It's kind of therapeutic for me at times, because I can get thoughts out on here that I can't really discuss with real people in my life. Most people on here are pretty tolerant and open-minded, so it's very refreshing to see that. Like another user said, it's an easy way to help get your voice heard (without having to talk a lot, for us introverts) and not have to worry about being judged harshly to your face. I also feel good knowing that I've given some truly helpful answers to people who are just as troubled as I am. There are some really wonderful people here.