A lot of them are staying in thailand and philippines. Just close a deal from US expat wanting to buy beach front properties of Mandani Bay in Cebu Philippines.
The income tax rate in Philippines is around 32%. It is close to the rate within the United States. So if someone renounce his citizenship, I am not sure how much he is going to gain in terms of savings. And also, once you renounce your American passport, it will be extremely difficult to get it back at a later point. A Filipino passport is useless for international travel.