This has been happening consistently since I first bought the n800 in January. I power down the device, it shuts off and then it powers back on after about a second or two. I then have to turn it off a second time after it completly boots to keep it from turning on again. Essentially, I have to power down two times in a row to keep the device off. Any ideas? Hawrdare problen or just a software bug?

That has not happened to me. My advice is re-flash the device and if that doesn't work, exchange it. If you bought it online in may be worth it to contact Nokia first.