I like em dashes, and use them when writing (or preserving the style of older books when I’m formatting them), but they need some taming for the Kindle, as discussions on MobileRead will show you. If you attempt to insert them between two words without any spaces, the Kindle will stubbornly keep both words together when breaking lines. A simple way of getting round this would be to use a spaced en dash instead, as Jaye Manus suggests, but can we do any better?