I've used Sun workstations and servers for a long time, and have quite a bit of UltraSPARC hardware, including a small quantity of the 'Panther' board, which puts a 'better than Ultra 10' UltraSPARCIIi on an ATX-compatible board. I even have some of the very hard to find PS/2 keyboard and mouse port brackets. The Panther (501-4559) board is a nice board that fits a standard case.
I have a couple of larger SunFire machines, a V480 and a V490. I think the V490 has four CPUs (two CPU/memory modules), and the V480 has two CPUs (one CPU/memory module) and I think they're both 1.5GHz. These machines are quite heavy. I also have a smaller V240, but it is pretty heavy, too, about the same as a Dell or HP server of the same size (V240 is 2U)
$dayjob has a few larger Enterprise series machines, an Enterprise 5500, an Enterprise 6000, and an Enterprise 6500. The 5500 and 6500 are in the full-height Sun rack, and the 6000 is in the shorter mid-height rack. The 6500 was last run about five years ago with a Fedora 12 install on 16 400MHz (501-4995) CPUs and 20GB of RAM. These require a 30A 208 or 240 VAC single-phase circuit; a lot of electricity for less real power than my Dell R710 (12 cores (two six-core Xeons) with HT (24 threads) and 96GB of RAM with two much smaller regular PC-style IEC C13/C14 receptacle/plug pair.
But they are fun machines to play with.