So earlier this summer I learned how to use RequireJS + a smidgen of Grunt, then I felt the need to move towards Gulp and Browserify (which I've just recently started), and now I'm excited about Duo.
It would be interesting for someone with more expertise to do a compare/contrast further down the line of all three.
"...I show you how deep the rabbit hole goes" - Morpheus
Also, does someone know how the Closure compiler fits into all of this? It might be totally unrelated but I'm trying to learn more about JavaScript application architecture, and I'm not sure where that fits in.