New vs Used when buying please share thoughts

Hi!
I would like to get peoples thoughts on new vs.used equipment. Is there anything you should not buy used such as speakers due to warrenty loss etc.. I am in the begining stages of setting up a system. I thought why not pose the question before I get knee deep in the buying process. I am new to the hifi world, and would like the comments from people who are in the know. If used is the way to go is Audiogon the place to buy it? Are there any pitfalls I should watch out for? I want to thank people in advance for responding to this thread. I think your responses will make my decision clearer. Again Thanks to everyone.