We are working towards ‘hopefully’ having bbPress ‘responsive’ with version 2.4.
You can see the details and where we are at already with this here.
It would be great if you could help test and contribute some feedback regarding this 🙂
You could always create your own BP child theme and use a framework such as Twitter Bootstrap to easily make BP responsive
http://twitter.github.com/bootstrap/
https://codex.buddypress.org/legacy/building-a-buddypress-child-theme/
This approach worked well for me.