Americans Moving (Moved) to England/UK

A question I'm interested in as well.

My wife is British, though not English, and we are strongly considering UK as a place to settle. I do like London, though I have reservations and ultimately it will come down to quality of life comparison.

The three most important ports for us are also roughly evenly distributed by flight time from London, so travel is less of an issue. Daily living expenses are relatively high, flats and houses are generally smaller with fewer amenities than similar cost accommodation in the US, the potential exists to avoid the cost of a car though it is unlikely we would forgo owning one. There are other more personal things as well, like the love of sunshine in California, mom's vying for access to grandchildren, love of the outdoors, etc...but those are less quantifiable, though at a personal level possibly more important.

Previously mentioned considerations aside, the most important issue in my opinion is lousy US citizen tax law. That is really the crux and something I know relatively little about. I understand there is an $80k or $90k living allowance write off, but I'm not entirely sure how that works. At its root, if there is any form of double taxation, it will be extremely difficult to make living in UK pencil. I would like to save a great deal of my income over the next decade to fund investments that will hopefully provide the real wealth for our family.

What are your pros and cons? Anyone share more light on US citizen taxation abroad?