I thought I'd share with you some questions that we've answered recently for colleagues.
Q: How are you cross-device testing?
A: We're using test devices and Adobe Edge Inspect (formerly Shadow.) At the start of a project, we look at existing analytics to determine the audience's most common devices, and then we seek out the ones we don't have. One tip to keep costs down is to purchase bad ESN devices from eBay.
Q: How do you keep from downloading hidden content on smaller screens?
A: Load auxiliary elements conditionally. Start with the mobile site as your default CSS, then use media queries for the larger desktop versions.
Q: How do you handle cross-browser compatibility?
A: HTML conditions for browser-CSS when possible. This reduces loading time for non-targeted browsers.
Q: How many form factors do you follow in RWD?
A: We let content determine breakpoints, not device viewports. We try to get as close to a fluid layout that works on everything as possible. Some people call picking device breakpoints instead of content is "adaptive design" not "responsive design."