The UltraSPARC Architecture 2005 specification (and an implementation supplement for UltraSPARC T1) were posted several days ago, on this web page:
http://opensparc.sunsource.net/nonav/opensparct1.html
Feel free to download them and browse away!
Note that those versions cover the Nonprivileged + Privileged levels of the architecture, which is sufficient for porting an operating system to run on top of the Hypervisor firmware.For those (very few) who actually need to write hyperprivileged code (a Hypervisor), full versions of the above specs that also include all the detailed hyperprivileged mode info will be posted in February.