Facebook Comments - 100% width

David,
Unfortunately, no. Facebook's comment box accepts only a fixed px parameter, not a percentage. There are some ways we're looking into getting around this, and we actually had a 'fix' in a previous release.. however, the minor CSS change we tried wreaked havoc on a lot of the other social widgets (Like button and others).

We're in the process of redesigning this site into a responsive template, so we feel your pain, and hope to have a good solution implemented in an upcoming release.

Thanks,
Alex