I can say the expat experience is part of why I am leaving the firm after four years in the US office. Typically the UK or international office of a US-based company offers far less room for promotion. They tend to be smaller, with the interesting changes happening back home. The friends I've met outside work have been American. The British seem to have established social circles they are not looking to expand.
People seem to work less and see their evenings and weekends as sacred.
Living in a different city and having to adjust your business style to suit the corporate cultures of various industries and countries. Dutch businesspeople are very frank. The French see Americans as a font of all knowledge and are not always satisfied when they learn that you only do a portion of what they expected. Healthy food, clothes that fit, reasonable prices, driving and my own furniture.