Since the internet spans the globe, it's important to remember to think on an international scale. Here are some netiquette issues that cross-cultures.
This is especially important in international correspondence. With differences in time zones, not to mention a variety of international holidays that might interfere with business hours, always give your recipients an extra day or two (longer on the weekends) in order to respond to your messages.
The date and time are not the same everywhere on earth, be sure to convert the date and time of your message to your recipient's time zone. Also include the conversion for any currency or financial figures mentioned in your correspondence.
As with all your professional correspondence, provide any available contact information. Be sure to include international extensions on telephone numbers.
Humor / Sarcasm
Different cultures have different values. Be overly cautious when using jokes or that 'dry wit' everyone at the office admires in your correspondence. You never can tell what the reaction to your punchline will be overseas. Keep your messages brief and to the point and you won't have to worry about bad jokes creeping into your documents.
This refers to thinking of one's own culture or nation as superior to others due to lack of knowledge (or ignorance) of other cultures. It has been my experience that I and other Americans are more commonly guilty of ethnocentrism than other cultures on the internet. If your swapping E-mail with a Czechoslovakian and start raving about Martin Luther King Day and the 1st Amendment, they aren't going to have the foggiest notion of who this Martin character is or what an Amendment has to do with anything. Remember to speak in an international context in your correspondence, and provide a small amount of background material whenever you refer to culturally specific people, places, or events