Looking at Fedora 14 and Ubuntu 10.10

> Spice sounds like a re-implementation of the thin-client concept, except it's a remote thick client...

Yes.

> Seems to me like there are other technologies like LTSP or Citrix that accomplish similar things.

Not really.

It depends on your goals. Do you want to provide a bunch of people some GUI applications so they can get some work done? Then, sure, you can use LTSP.

Do you want to give your users access to a OS were they can have a set of applications and be able to set things up for themselves without your intervention? Do you want to allow them to use Windows in a thin client setup? Do you want them to have access to multiple operating systems?

Then you'll want to use KVM/Linux + Spice.

As KVM matures your gaining access to a lot of features like 'deduping' memory (so you can do something like run multiple copies of Windows from the same section of physical RAM). That way you can over commit resources to your virtual machine and economically provide multiple copies of the OS to a large number of end users on a large server machine. It's not as lightweight as doing containers or just going multiuser on a box and doing X networking, but it's not nearly as expensive as it once was.

Spice depends on paravirtualized drivers and KVM to create a GUI were you have some actually really good compresson over a network. Performance of it is much better then Microsoft's Rdesktop (RDP) or Citrix's ICA remote desktop protocols and will usually perform better then X11 networking.

It's very neat and is needed as corporations are now leaning much more towards virtualization + full desktop + remote GUI versus the old thin client scemes.

Spice is a much more efficient replacement for RDP and VNC. Although it can be used as part of a thin client solution, it was designed for VDI. It was a proprietary protocol developed by Qumranet, original developers of KVM. Their business plan was to build a management layer on top of KVM and use spice to remotely manage Windows machines. Red Hat acquired Qumranet and recently open sourced Spice under GPL and now it will become part of the Fedora 14 release.