I don't personally, but I can see why others would. Take gaming forums, for example: let's say there are four nodes, one for PlayStation/Sony, one for Microsoft/XBOX, one for Nintendo, and another for PC gamers. Having a unique style for each node can help create a visual distinction between each one (like a blue/black/white color scheme for Sony and a green/black/white for Microsoft).
That said, it does require supporting more themes and there will always be users who don't like one or another, so I can see why most wouldn't want to go this route.
i would definitely use it more if it was an 'initial style' and a user was able to override it with something of their own choice. but as it is its impossible to then give the user that choice.
too bad. it could have been a great feature.