My customers have serious complaints that they get this http://domain.com/domain.com_non_ssl all over the place. I have seen it myself a few times. Looks very unprofessional.
See my _non_ssl thread below, this is an architectural problem with Plesk, when using ASP apps it does not return proper variables for MapPath() and doesn't use WebSites the way IIS likes it to. This will be fixed in Version 7.0 in the mean time all of our sites we are setting up manually in IIS to get around this problem.