To me.... I thought they looked pretty professional, and so did the guy buying them. I just had the problem of painting them too fast, and not giving proper drying times. I fixed that after a dozen boxes or so.
I too used spray paint, Krylon for the actual paint, and automotive Clear Coat for the finish. I think it depends on their methods, but you can buy REALLY NICE spray paint, as long as you know how to do it properly... give the correct distance, sand between coats, sand after clear coat.. etc.
I also found this metallic paint, green red purple blue etc, and you just do a color underneath and then spray your metallic paint over and you get the different colors from different view sort of finish... that is what I had on there.
I had a green/silver xbox with a window, bright green LED's and a silver 12mm fan installed just about the graphics card heat sink, the one that pipes out from under the dvd drive.
I, for some reason, don't have any pics on my computer right now. will try and get one up.
I am sure it's against some sort of copyright, but I also made a Gears of War Xbox for a friend, and got a controller painted up to match it! Talk about a pain in the A$$.... But it looked bada$$. I REALLY need to find those pics! I have done about 12 xbox's and at least the same in controllers....