I first clapped eyes on Metafilter in 2004 or thereabouts when a friend loaded it to find a Flash game - it was in a thread titled "Friday Flash Fun". ("Ah, what a nice nerdy place, they have weekly Flash posts," I thought.) I was an introverted 15-year-old deeply involved in geekish fanfiction pursuits/LJ/deviantart, and thus the perfect demographic.
The distinctive blue background and name stuck with me; around the same time I started reading kottke.org and other blogs, but it was Mefi with the quality and quantity of its links and comments that eventually consumed a large part of my internet browsing time. When I left fanfiction and Hong Kong for good to study abroad, Mefi and Askme became irreplaceable sources of information and support for me. Initially I lurked because the content was freely accessible, but finally caved in 2008 when I had access to my first (subsidiary - sorry Mum!) credit card and hence Paypal :)
You're my favouritest American thing!
There are too many to recount! The sexism threads, the American political threads, the quirky, funny links to cats, indie artists and niche phenomenon, the amazing Askmes, even the frustrating 500-plus-comment arguments that go nowhere and make me confused about everybody's opinions including my own (often found in the first two types of thread)... a personal favourite is the breaking-news type of post: upon hearing some news story I immediately wonder what Mefi's take on it is. The Japan earthquake thread was the most coherent and comprehensive English source I could find online.
The site and coverage slant heavily American and occasionally that annoys me or other furriners - but I cannot thank everyone enough for showing me the good, the loveable, the noble, and the beautiful side of your country. The way everyone rises to the challenge and helps somebody in need on Askme. Some of the best and most moving pieces of writing I've read were on this site.
Thank you for teaching me that the US represents many, many things - some good, some bad; it's not just the caricature we from the outside looking in fall back so easily on hating, and the immense humanity we all are capable of. Mefi was with me through my most formative years, so it's no understatement to say it has profoundly informed my views on relationships, politics, and life in general. (And imagine, I just lurk!)
I'll probably not make it to the USA quite soon enough to meet every one of those familiar and well-loved usernames, so I can only wish you well from afar. Sending hugs and lots of cupcakes from Asia!