In writing you get told to focus on a single core idea: a central theme that you revolve everything else around. It works similarly for web design (or at least that's the model my cofounder and I are using): you find out what lies at the heart of your system, what everything else revolves around. Every idea has one, even complex ideas. You figure out how to create that idea, and in theory every feature you add should revolve around that central concept.

Sam: your idea is based around commenting, right? What you need to do is figure out exactly what your big idea is. It's never something vacuous: it's one specific thing that you think places you above the people who are out there now. Everything else you do revolves around that core.

(As for people to interview: you could always try the 37signals people, and I'd also recommend the contrast.ie team: They have a very good sense of how to focus a concept.)