I have pam_usb installed to authenticate via my usb key, and it seems to work for all things except for gnome-screensaver when it locks the screen (same thing when I switch users). It just asks for a password like normal.
Here is my /etc/pam.d/gnome-screensaver:
Here is my /etc/pam.d/common-auth:
auth required pam_unix.so nullok_secure
And, finally, my /etc/pam.d/usbhotplug:
auth sufficient /lib/security/pam_usb.so !check_device debug allow_remote log_file=/var/log/pam_usb.log fs=vfat