Yea this is an age old discussion, I also like the separation that dashes or underscores give. Personally I'm a fan of underscores myself, mostly because I can then have id="foo_bar" #foo_bar and $foo_bar, for html, css, and jQuery variables, respectively, and remembering that JS can't have dashes in variable names. This makes the double clickable aspect super handy to me :)

Sometimes I hear that people don't want to have to press shift, which is understandable considering how much we code. But if bootstrap devs are already pressing shift in order to use camelCase, I wonder why they didn't pick underscores.