There is a rule in the css file ".appnitro li" which sets the width of the fields to 61% of the size of the form.
This rule works when I am viewing the form in Dreamweaver, as well as when I preview the form in Firefox or IE. However, once the form is published, this rule doesn't seem to catch.
I don't know if this was intended or not. It looks a lot nicer with the rule in place. For instance, paragraph fields, and the address fields don't look right when they span the entire width of the form.
This shows up as well on the forms hosted on your site, so its not on my end only...