I have "Force SSL Administration" switched on which works really well to force SSL for the WP dashboard.
However I want to force SSL when logged in (pages, posts and admin) and to redirect to HTTP when not logged in (except for pages marked as SSL). I don't really want two versions of the site (SSL and non-SSL) to be available. Just SSL for logged in and non-SSL if you're not logged in.
I'm finding that if someone logs in on HTTP they get redirect to HTTPS and they're not logged in anymore. I don't know whether there could be some incompatibility with the "Theme My Login" plugin? I am redirecting subscriber users to a "members page" on the website once they log in- they never see the WP dashboard.