I've been watching/waiting for Yeoman for quite a while now. I can't help but wonder how much Twitter's Bower pushed you towards launching today. This looks to fit a lot more of the workflow than just package management though and does a lot of the things I'm currently doing myself through a huge mashup of other tools.

EDIT – totally missed that this in fact uses Bower for the package managment, so probably couldn't even launch until that was released.