Adapt.
I’m skeptical of anyone who can say they know the future of the web with a straight face. The coalescence of CSS, JavaScript, and server-side technologies in building websites is murky, unstable, and highly debatable. Depending on the needs of your audience, your capabilities, and the exact moment you deliver the site, you could justify almost any technology decision. “One web” sounds nice, as do exhortations to respond to varying browser sizes and browsing contexts. Unfortunately, clarity doesn’t appear to be imminent. Desktop browsers are iterating rapidly, mobile platforms are still in their nascency, and screens are being attached to new devices every day. Be aware of what’s happening, but don’t freak out if your attempt to embrace every trend and fad collapses under its own weight. You’re already building modern sites and apps with modern techniques. Leave the bleeding edge to the conference speakers and book writers.
Oh, and Nathan Smith has another tool for your belt: Adapt.js, a script that determines the width of the browser and helps you serve stylesheets accordingly.