Cards should be editable, at least for a short period of time after submitting. It really discourages a longer note to not be able to go in and fix typos. Then again, I do like the permanence of a MetaFilter post.
Yeah, I'm still wrestling with editing and permanence. Will definitely support editing if it's never been published and maybe a time-limit on editing once it has been published.
EDIT: editing is now supported.