For yafla registered clients (which basically means professional consulting clients who need the online tools) I've implemented an "AJAX" style logon (evident on the home page. It was basically developed for the upcoming http://www.360notes.com, which is currently in super-ultra-amazing stealth mode). It's responsive and extremely lightweight, and works throughout the site without redirects.
Maybe I'll bundle it up and sell it as an AJAX-enabled ASP.NET logon security user control!