I know a few people have had problems with the ethics of adding a US address to Amazon and some people dont have a problem - however rather than adding a 'random' address you can sign up for a free account at
http://www.borderlinx.com/
They offer a service where you can order stuff in the US , and they then forward it on to your legitimate address (for a fee)
I've never used it for that - but it is the address I have set with Amazon US the reason being that :
1) Its a valid US address in an area which does not get additional sales tax (I had previously set the US office for the company I work with but then Boston changed things and I found that Amazon had added sales tax to my purchases).
2) If you accidentally have anything sent to that address then Borderlinx will send it on to you
3) Because of what they do if anyone at some point in the future wants to check up on the address you have supplied then its a legitimate address which can be used by you (for those with random addresses set I worry that at some point Amazon will start trying to verify them and find all these people staying at strange hotels or airports
4) If you have a problem with signing up using a 'fake' address - this is not a fake address its a real one and its tied to your name and your 'real' address