My wife & I (we've lived in America since 1991) are thinking of retiring in summer 2010, spending extended periods in the UK next fall, and possibly buying a house in England as a second home, with a view to thinking about becoming resident in the UK sometime over the next couple of years.
She's a US citizen, born & bred, I'm a dual US/UK citizen, originally from England. Our children have been gone for a few years; one lives in London now, the other in Massachusetts. We lived in the UK 1973-1976, US 1976-1979, UK 1979-1991, and since 1991 in the US.
We've lived for 12 years in a small rural town that makes sense for our current jobs (prison & college respectively) but makes less sense in retirement because we don't really have close friends here. Britain strikes me as being more "senior-friendly" than the US (walkable towns and cities, good public transport, milder winter/summer weather, National Health Service, interesting places to visit & vacation.) I realise that a lot of this is subjective...