thanks to Mindy for one of the all time great threads. To add a few to think about:
*(on religion) If you are a devout Christian, think about what it means to live in an extremely secular nation (even despite the lack of a Church/State split). If you're Jewish, think about what it means to live in a nation where the general tendency is towards support for the Palestinians and there is a great deal more criticism of Israel than is so in the US.
* If you've visited England before, was this only London? Keep in mind that just as NYC and LA are very different from the US, the same is true for London and the rest of the UK.
* Can you recognize that coming to the UK means not only having to learn another culture, but also learn to negotiate a culture that is itself in a process of great transformation? Despite it all, life in the UK is rapidly changing and so are people's perceptions. Not too long ago, Brits rarely shopped or lived on debt: all different. Not too long ago, homophobia was tacitly acceptable, no more, etc. You might be looking forward to coming because of happy memories from 10 years past. This might be impossible to recreate because those days are gone for the locals as well.
* How computer literate are you? If not very, then try to learn, since there's so much of US culture that is available in ways that weren't before - newspapers on the web, tv shows streamed or gotten via bittorrent, net phone calls. If very, then also keep in mind that net culture works differently here than the US.
* Can you also recognize that you're not only moving to the UK, but to Europe as well, and that you're not only going to be integrating to one national culture but a newly developing nexus of many?
* Can you differentiate criticism of the current US govt from anti-Americanism? This is a great roasted chestnut on the forum, but generally most people here think poorly of the US govt, but also differentiate it from their perception of Americans and American culture.
* Can you understand the difference between other expats dislike of some things American and their appreciation of others?