One thing that FW 2.3 did for me is "fix" my version of The Good Shepherd HD DVD. Apparently there is an exchange program for the title, but after the FW 2.3 update, the disc played fine all the way through tonight. Before, the same disc would throw an error and simply not play.
I used the downloaded FW copy from the Toshiba website on my HD-D1 and updated via CD, FWIW. I also cleared persistent memory and soft-initialized the player as suggested by others, although I don't know if these additional steps are critical or not.