The English speak English, and I can't think of any serious socially-oriented sites that are popular across the English speaking world that were born in the UK

The English speak English, and I can't think of any serious socially-oriented sites that are popular across the English speaking world that were born in the UK except for last.fm which was mostly a music tracking service than a social area. I'd be interested if anyone can bring any up though, but I'm kinda surprised nothing like a British version of Reddit ever took the Internet by storm.. everyone I know here just uses all the American sites.