Same problem, I upgraded from Gutsy to Hardy 8.04. Originally I didn't have the login problem but I did have a lot of trouble getting the initial upgrade to work with my video card (NVIDIA Quadro 4 280NVS). After I changed the video driver from nvidia-glx to nvidia-legacy, my video worked, but the double login started.
Same problem, I upgraded from Gutsy to Hardy 8.04. Originally I didn't have the login problem but I did have a lot of trouble getting the initial upgrade to work with my video card (NVIDIA Quadro 4 280NVS). After I changed the video driver from nvidia-glx to nvidia-legacy, my video worked, but the double login started.