The Importance of Flexible Content
Jeremy Keith writes about why we shouldn't be designing around "common" breakpoints. He advocates instead crafting the design and its behavior at various sizes around the needs of the content, rather than picking breakpoints that, while seemingly logical today, are in fact arbitrary and will in all likelihood be much less relevant a short time from now.
I agree wholeheartedly.
Taking this approach a step further, we should be insisting on flexible content. If the content is inflexible, then it won't be able to adapt and flow into the numerous layouts necessary for today's devices, much less the multitude necessary for the devices of tomorrow, next week, next month, and next year.
In conclusion, don't just design with content in mind; create content (or collaborate with those responsible for creating content) with flexibility in mind.