Lately, for myself, none. The tinkering I do these days is if I'm helping someone and I don't immediately know the answer. When I was more in to theming, I could easily spend the majority of a day messing around with Litestep. The last thing I was messing with wasn't actually a theme. It was a setup that works perfectly on top of explorer (I wonder what the legalities of releasing something like that would be?).