What surprised me is that Fotolia is even better (in terms of sales) than IStockPhoto and Shutterstock - at least for me.
I don't know why but I would advice it's because it is localised in many countries and it sells worldwide.
Keywording is essential. Your keywords are automatically translated in many languages but of course there's the risk that automatic translation isn't perfect so I prefer to keyword my pictures in English even if my main language is Italian: at least most of the people in Europe and US will find the right words.
