snupy, the tax stuff...the first step is informing them that you have a new address. You can do that once you get settled and then go to the US Embassy in London. While there you can change your address with Internal Revenue and Social Security. (I also needed to change my name on my passport and that was the main reason for my visit.)
After that, the IRS will send you your next income tax forms to fill in. Then you just file as usual. There will be some slightly different issues to deal with, so you might want to get some professional advice.
It's not that difficult to keep it up, it's just that I was told there I didn't need to file if I earned less than £x. I was told wrong. And I think a few others got tripped up as well.
And the will, apparently the US won't recognize a foreign will, and it will tax inheritance. So, they will see it that you don't have a will, and take it from there. Whether they are nice and generous, or mean and money-grabbing, I don't know. Not having a will does not mean the partner automatically gets it. I was told in the UK, the partner gets the first £125,000 and the rest go to the children...if there is no will. And that is just one for instance.
My guess is that it's a simple enough procedure...have a will made up here, then take the same exact wording to someone who can file it in the US. I'm still looking into this one.
Anyway, I can't see there there's too much complication in any of this, it's just that if you don't know and do it differently, or if you just figure it's going to go away and it doesn't affect you, a small amount of work on your part to make it right could have a significant benefit. Doing nothing may make things really really hard. And you don't know what affects what. Could not filing taxes mean you can't vote, for instance? It certainly means you can't collect social security...not that any would be left, but I worked for 25 years in the US, and that added up to something.
As I said, I'm in the process of getting some of these questions answered. My head spins at the moment, so I might be fuzzy, and in some cases wrong. Frankly, the guy I spoke with the other day didn't have a clue about how the US does things, but he threw up enough warning flags for me to go "oh s**t" and to start looking into it, trying to get things on the right track.
I hope we can all keep expanding on this, and then come up a clear, concise checklist for those who follow on. Like I said, it's not hard...but it does require knowing about it.
(Whoever came up with that phrase "Ignorance of the law is no excuse" must have been a souless jerk. Sadly, a line has to be drawn, otherwise you'd have murder trials with people getting off on "gee I didn't know killing someone was illegal in this country.")