Although reading this site has affected me a lot in large general ways, like Deffeh I've become a lot more interested in politics and social issues, I'd say the biggest impact it's had on my life was from a small thread Nodrog made nearly three years ago.
This thread to be precise. Nodrog has always been one of my favourite posters in the years I've spent here, predominantly lurking of course, and on the basis of his praise for that film I diligently tracked it down to see why he rated it so highly.
Suffice to say I was blown away, three years and many hundreds of movies later All About Lilly Chou-Chou is still my favourite ever film, one of the few that I watch whenever I'm sick or feeling down. If you've ever seen it you'll know the movie relies heavily on music, in particular some of Debussy's piano pieces and this led to me starting piano lessons and I'm now fairly decent and it's a pretty big part of my life, I took my grade six last month and I should get the results back any day. There's no way I would be doing that if I hadn't read that one thread.
I've also learnt a lot more physics than I otherwise would have (Thank you MrL_JaKiri).