I’m old-fashioned and still write the date: 6 November 2010. I have recently started dropping the “th” from 6th. If you’re American, you’ll write it differently: November 6, 2010. As for what to write on the board, it is helpful for students to see the date written in full. It will serve to remind them how to write it out. I find that many students, even at intermediate level and above don’t know how to write the date correctly. It will help them remember, if they see it written in full every lesson. Having said all that, if you have a small board, there is no harm in writing 06/11/2010.