I must add that some of the equation has to do with how you feel about life in the U.S.--it's sociology, politics, popular culture (in the broadest sense of the term), etc. Probably the less enamoured you are with these various aspects of the U.S., the less homesickness you'll experience, and the less desire to return to the U.S. However, the move is still likely to be a significant displacement - a realisation that may only dawn over time -even if you previously spent a lot of time visiting over here and trying to immerse yourself in British culture (broad meaning, again). It is true that - especially for persons who are a bit older and bit financially established in their lives in the States - moving to the UK is probably going to involve a lowered standard of living, decreased spending power, and worries about the quality of healthcare and elder-care. Cultural differences are subtle and pervasive -IMO- but you are likely to only become aware of these gradually, because they represent stylistic differences. The obvious stuff that you can easily see isn't important, and I'm amazed at the amount of whinging about trivialities that I read in this forum. It really is things that are more difficult to put your finger on (ways of working, personality and interpersonal style, approaches to practising certain professions, etc.) that can be troubling and less readily resolved than the fact that you can only buy small tubes of toothpaste and that "fortnightly" indicates a frequency of every 2 weeks.
BTW, me--I'm sick of the U.S., but some things like financial realities are hard to argue with.
