I've been using FreeNX now for quite some time.
An interesting 'twist' is if you've deployed a 'Virtual Private Server' on the net (www.linode.com for example), you can set up a KDE desktop and NX to it on the Net!
I'll let that sink in.
Expect to see the VM/VPS Virtual Desktop market 'propel' forward with NX behind it!
Thanks Tom for highlighting this 'thin client' revolutionary technology!