filenames - How do you manage images with duplicate file names in Lightroom?

I've had my camera for about a year, and having taken 9999 images the camera's file naming system has rolled over to 0001..

I usually import my photos to Lightroom, so Lightroom sorts them into different folders based on year..like 2010, 2011, and then into further sub-folders by date.

I am doing some stock photography, so I am exporting all the final images into a same folder. Since some of the images will have duplicate names, there is a risk that I will overwrite files on export.

I would like to know how you handle this situation? do you use a specific naming strategy, or just simply put everything into different folders on export?