I saw a very interesting documentary on the Discovery channel not too long about this. From what I remember, it was highly recommended that adults get at least 8 hours of sleep per night. And although they said that taking "power" naps was good, they should be limited to 20 to 30 minutes. Also, they said not to consider, ..."hey, I don't sleep too much at night, so I'll just start taking naps everyday." The scientists involved in relaying the hard data on this show made it abundantly clear that these naps do not make up for loss of sleep. They also recommended to those of us that do not get enough sleep per night, to learn different relaxation methods. Apparently, your brain responds well to deliberate quite/down time, as does your body. Many people believe that sleep is in fact a method of relaxation. They stressed that it is not. For those interested in learning more about this, I'm sure you could do a search on the Discovery.com web site and maybe even score the VHS/DVD version of that aired show.
Good thread!