I have worked internationally, and have had no more or less issues with them in comparison to domestic clients. The biggest barriers are payment, which these days Paypal and the like are there to make it affordable and easy.
I work with domestic clients without ever meeting them face to face, and in the world of the web some clients expect this. Some clients expect someone local, and some just want someone competent no matter where they are. Marketing yourself to the latter group is very important, and I suggest that you do it.
As always, watch for dud clients, which sometimes are harder to spot in the international scene. Also I recommend avoiding clients who have difficultly speaking or communicating in the same language, and any clients who give you reason to question them.
jeremy - gnomeontherun
Educated questions often get educated answers, and simple questions often get simple answers.