Mirror Site Question

I have a question and it bugs me much, its about mirror sites. im kinda new to this approach and wanna know some facts about it..

im handling a business niche site, but it has duplicate site which is really copycat of everything except the url..both sites owns by one owner..my question - should i continue working with the main site ?? and would google penalize us?

any input would be greatly appreciated. Thanks!!

As long as the both sites are owned by the same person/company you should be in good shape. There are several reasons for mirroring sites most of which are fine until you start breaking the law, that's when Google will notice.. even then if it's not affecting them they may not give a damn