I'm seeing the wrong permissions on installed components, likely based on a bug here:
Unless I'm not using components as they were intended, I've simply run:
yeoman install ember
and all scripts 403 due to the folder perms of each comonent.
I'm running into the same issue. If I "chmod -R 777" the components folder, it works fine... but if I run yeoman update for example, it resets all the permissions, creating the 403 errors again.
We've upgraded Bower in master. Fix will come in yeoman 1.0. Soon.