Another distro of linux now supports the UltraSPARC T1. Here's the press release from the Gentoo Engineering Team, Gentoo Linux 2006.1 Unleashed
The SPARC release includes several improvements over 2006.0, including InstallCD support for systems with more than 4GB of memory and an updated toolchain bringing fixes for various compilation problems. Also new is InstallCD and kernel support for the new UltraSPARC T1 processor used in the Sun T1000 and T2000 systems.