"Subscribe To Thread" is handy in that it can be used with folders to store things in your usercp usefully but no it doesn't store a specific point in a thread.
"View First Unread" is good but can suffer from an obsolete third-party cookie bug if you share a computer or log in/out. Can usually be fixed by manually clearing all atnation.com & related domain cookies.
Bookmarking a post within a thread isn't out of the realms of possibility and a not bad idea if anyone finds/makes a plug-in for it
