Sovereign immunity for Indian nations is a hot topic these days, at least with respect to patent law. I posted about tribal immunity back in 2011. The post was focused on tribal immunity from patent infringement, rather than immunity from USPTO actions. You can view the post here: [Sovereign Immunity from Patent Infringement for Indian Tribes].
Looking back at that post, I thought people might be interested in listening to the oral argument from the Supreme Court case Kiowa Tribe of Okla. v. Manufacturing Tech., Inc., 523 U.S. 751, 754 (1998). You can listen to that oral argument here: [Listen][Read].