Looking over the discussions and Trac tickets am I correct in assuming that the simply_helpful's form_for not respecting the default_url_options (specifically only_path) is a side-effect of some other default behavior choices?
Personally, I set only_path to true as my default as I think except were you are dealing with https it makes life much easier (especially in testing) and is just cleaner all around. I've always hated unneccessarily qualified links, as they can bite you in the ass.
If I could track down and modify this behavior, would there be enough interest in it (it may be right at the edge of my ruby-fu) to get it patched in? I know the usual answer is "make a plugin," but I don't know if I really would want to maintain a plugin for a plugin.