As I'll point out again, Sun has had this technology for years.
Same for the OS that ran on the Tandem boxes. The thing that has me excited about the Proliants getting it though is that it has now dropped enough in price that low end servers (albient mid range intel servers) can easially put it in the box without increasing the price over the last generation box.
I'm now wondering how long until hot pluggable CPUs exist in low end servers.
Also, the most likely OS to add the hot add memory on the machine above will most likely be a UNIX based one anyhow, as I didn't see a hint of .Net supporting it.