Being from the EU, I've got the idea that most people are pretty attached to their currency. I'm guessing it depends a bit on your market - some people (global-minded?) have no problem doing currency conversion, others do (nationally-minded?). For a company selling a downloadable program, I had to modify their website so it could sell in these three currencies (EUR, GBP, USD). Since they have no official presence there, I presume it was feelgood only.

I suppose the question is not "should you" but "can you afford to". If you can make it so, reaching out to the customer, "speaking" in their own currency, is always a benefit.

Edit: If you /need/ to pick one, pick the one were you expect the most revenue? I don't think anyone of them are less hesitant about it than others. Save for maybe EU people since they might remember the good ol' days of the Mark and the Franc and such.