I learned about NewGrounds from various Newgrounder's that had also started making YouTube channels back when YouTube-NewGrounds video theft was more frequent.
I watched the Awesome Series, Brawl Taunts and various others NewGrounds classics when I was told I could watch them on the site in crystal clear quality.
So I've been coming to this site to look at videos and games since...2008 I believe. As a result I've found some really cool submissions and users who's work I still follow to this day.
The thing that made me make an account was my own laziness. I've started a large array of different projects with Flash and I've been juggling all of them. So everything is getting worked on a little bit, but none of them are getting my full focus.
I figured that if I joined some contests and collabs, the requirement to finish a project before a deadline would be the driving force to make me finish something from start to finish, and get the creative juices flowing to the point I can start working on my gigantic pile of animations.
NewGrounds is hopefully the medium that will get my lazy butt back into animation mode again, and the collab I'm participating in should see to that. :P