What I'd like to see is a comparison of the commercial NX (and any of the free projects that come from it) to the SPICE protocol developed by the Qumranet folks and currently being integrated into the upcoming RHEL 5.4 release.
According to a SolidICE demonstration video from some time ago on the Qumranet website (http://us.qumranet.com/videos/Qumranet.wmv), they claim the SPICE protocol can do a four head display, support bi-directional audio, and full screen HD video on one of the displays... at local computer speeds. Of course that is over a LAN but one would hope that it work well over WAN sans multimedia. The SPICE protocol is patented but hopefully given Red Hat's track record they'll open up the protocol with a reasonable license? SPICE is being used as a delivery method for KVM-based virtual desktops but surely it could be decoupled and made into a general purpose remote desktop type client/server scenario.