I do not know many guys running FreeBSD on SUN hardware but I do know of many OpenBSD guys running SUN hardware. OpenBSD has by far the best support for SUN hardware of any operating system short of Solaris. OpenBSD does support mutlithreadinleg on sparc64. The only problem I can think of from the top of my head with SUN blade 1000 is that some blades if I remmeber correctly have hard drives attached with optical cables instead of SCSI controllers. You will save your self a lots of trouble attaching your hard-drives as external hard-drives via SCSI.