As JF said, you can't really fully judge the sheet UI idea until you see it in action for yourself. I'm one of those people who opens a new tab while using Basecamp for each item of interest. To me, these sheets could either <i>solve</i> that for me, or create an entirely new problem where it becomes jarring if I still prefer my old habits.<p>The one thing that stands out for me is how this effects the developers who work with the Basecamp API to bring the same experience to mobile, or other devices. I feel like developers who make a Basecamp app for iPhone, for example, are going to struggle trying to find a way to make these UI elements work the way they have been intended. And yes, developers <i>will</i> try to emulate it.<p>I'm reserving judgement, but for those working to bring an experience like the web-based version, I think there will be some long-game challenges. We'll see.