As of now, in order to ensure legal compliance, we work through another company for hiring outside of where we're officially incorporated. Because of this, it's just too expensive for us to hire people elsewhere.
This is beyond the timezones and other logistical issues, of course.
Anyway, I know so many people in Europe who absolutely love Khan Academy. Keep that in mind when thinking about expanding your talent pool :).
Also keep in mind that if you can hire in one EU country, you get access to the talent pool of the whole EU, since I can just show up in any EU country and start working.
Cheers!