dd/mm/yyyy on paper, but if I'm writing for online consumption I write it long hand, like 25th October 2010 because otherwise those who write it in the strange and counter-intuitive way will get confused, and I desperately hate trying to work out what dating system people are using so I am considerate.
Honestly I think we should all jump up and down on countries that write the date the wrong way (i.e not dd/mm/yyyy) and do not use the metric system (all three of them)... that's a way I could get behind >.<