I've been bored the last few nights and did a quick mash-up of a site-wide skin like the one that is on the home page. There are A LOT of things I would change if this was ever actually adopted, but I think you can at least tell whether or not it's a decent or terrible idea by using it in its current form.
There are a lot of positives and negatives to using it, and I won't bore you with most of them that you wouldn't notice. I think the main thing is that navigation would be consistent across the entire site, which honestly, is one of the most important things a website needs to have. Of course, the point is moot if it's so ugly people just instantly shut off their laptops when they see it.
You can try it out by going to the bottom-right of the page, select "Change Theme," and then click "Developmental."