I have written before about Amazon's Kindle Ad Units - which are usually excellent. Here is the latest - and you will notice the similarity in prior units. Nevertheless, I love the tagline "Buy Once, Read Everywhere" because: 1. it sums up the Kindle's value proposition perfectly (they won't win on device, but portability is a big positive)

2. it leverages the success of other platforms - namely Apple (iPhone, iPad, Mac) and Android

3. it sums up so much of what consumers, publishers and developers alike are facing: the multi-platform conundrum (ie write once, read anyhwere)