Around 20-25% of my sales are to international clients as large letters, usually untracked. The loss rate is definately higher than Australian sales and has increased quite noticably in the last six months. The margins on the items I sell range from 500% to 2000% so i can afford to lose a few, but items going missing is definately becoming quite a problem with international sales.

If you are working on profit margins of less 300-400% it could become pretty maginal as evey time you lose a letter, you lose the postage cost as well as the item.

edit, - all of my items go standard international flat rate. Maybe that is part of the problem