I think it's always good to have a couple friends or co-workers take a look at it but you don't necessarily have to have people at a studio master it. My brother and I occassional pass masters back and forth from our studios and get fresh ears/speakers to listen. As a matter of a fact, I often will not let him hear what I am working on until it is completely finished for this sole purpose. He works for a studio in nashville and I have access to the mixing booths at the radio station I'm at right now, but we both feel fairly comfortable mastering in our homes. In all honesty, I do think that having either A. A car with a really good stereo system, or B. A set of studio-quality monitors is a must.