Oh for god's sake, KEEP ME LOGGED IN.
And if not, at least take me to the page I request after your login screen. For example, I keep a bookmark of the Script management page (http://userscripts.org/home/scripts). But, it often signs me out and redirects me to the login page. Once signed in, it takes me to some other page and not the page that I had requested. This is not the way most other websites behave.