A big part of learning how to use WordPress is learning how to do things: one of the best ways to do that is to pull themes and plugins apart and see how they work. There are some great themes and there are some rubbish themes: the more you look at, the more elegant solutions you find. I’ll admit I didn’t really get the big deal behind the twentytwelve theme, and I was distinctly underwhelmed by the underscore theme – though I learned a lot from pulling it to bits.
The upcoming twentythirteen theme is different though – I really like the way it uses post formats and can see how you can abstract a lot of formatting decisions that I used to make on a category basis.