The major mistake that US executives make is not understanding enough about Europe as they try to attack the markets here. Learn about your markets, and you will be far better suited to meet their needs. Don't learn, and you will simply be guessing. As simple as this sounds, we have seen a number of US executives attempt to conquer Europe without spending the time to understand the very basics of the business environments here. They simply don't understand much about Europe at all.
Online companies have to work within the local culture.
Pure translations of US websites by themselves simply don't work. First of all, the European online world is not substantially Americanized. But even considering the small state of Americanization right now, the trend is absolutely to become less Americanized. The increase in number of online users means increased demand for local content and services. That is, content and services created and offered by business that really understand the local needs, customs, requirements and preferences.