As a permanent resident living in the US I find myself wondering if it thusly makes sense to never take US Citizenship. It seems like I can easily abandon my residency the moment I want to retire and leave the US. Am I missing something ?
It's more complicated than that. If you've had the green card more than (I think) 8 years you will be treated like a citizen should you want to give up the residency. So you have to pay the exit taxes (mentioned somewhere else in this thread).
Permanent residents are also subject to the expatriation tax AFAIK.