The site popped for me here in the USA. 😉 I ran your site through GeoPeeker and saw the difference in load times depending on location -- with USA being the fastest. But it did show that the screen shots lagged quite a bit when all locations were trying to access.
Did you look at your YSlow score? The first 5 "F"s could directly impact users. Particularly a CDN. Maybe try resolving those issues and see if the situation improves?