For anything handwritten (cheques, dates on signatures etc.), I use YYYY-Mmm-DD (e.g. 2012-Jan-10), as I can't imagine anyone confusing the meaning of it. I avoid DD-MM-YYYY and MM-DD-YYYY, as I usually end up having to check what I meant. No one has commented on it yet.

Typed, I use YYYY-MM-DD (e.g. 2012-01-10), mainly for its sortability.