It really surprises me how common that mis-perception is. Almost everyone I know who I mentioned that I will try and get my UK citizenship in three years of moving over says "Oh, won't you lose you American citizenship." It is really a huge urban legend these days. Taking on another citizenship did cause issues back in the late 70's early 80's but all that stuff has been worked out now.
There are only two things that "might" make you lose your citizenship, but even then they are somewhat gray areas. First is serving in voluntarily in a foreign military, or taking public office where you set foreign policy. The only way to be assured of losing your citizenship is to go to a US embassy, hand over your passport and denounce your citizenship.
Now you can lose your permanent residence status by staying outside of the US for a certain period of time.
Of course there is the whole issue of where you are domiciled does have an effect on matters of inheritance and can be effected by how long you have been out of the US, but you can easily be a non-domiciled US citizen. Of course lets hope you haven't gotten quite yet to the matter of estate planning!