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 Base

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 solve that for me, or create an entirely new problem where it becomes jarring if I still prefer my old habits. 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 will try to emulate it. 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.