Good Linus quote:
Nobody should start to undertake a large project. You start with a small trivial project, and you should never expect it to get large. If you do, you'll just overdesign and generally think it is more important than it likely is at that stage. Or worse, you might be scared away by the sheer size of the work you envision. So start small, and think about the details. Don't think about some big picture and fancy design. If it doesn't solve some fairly immediate need, it's almost certainly over-designed.
I don't find the "most widgets are trivial" argument compelling; the large portion of the internet devoted to porn doesn't detract from the rest of it, and likewise, the uselessness of unpopular widgets doesn't detract from usefulness of popular ones.
I really like Google's widget advertising service that let you dive deep into content without leaving a page. For example, I watched all 6 video clips on a National Geographic widget ad for their new "6 degrees" show. I'd have never navigated to another page to do the same thing.
I think we're just at the beginning of widget up-take... but I could be wrong, and would like to hear the arguments from the other side (perhaps there good discussions of this elsewhere already?)