I have used the redhat version of the Linux Terminal Server Project (LTSP) and the Ubuntu version of LTSP. This thin client solution works very well.  It is free and open source, but requires a fair amount of administration, setup and configuration.  If your network is solid, LTSP is very stable. Using LTSP is not rocket science, but it requires a fair amount of technical expertise. It is well documented online, and the project community will answer your questions.  Students adapt to thin clients readily, the adults will take longer to stop complaining.

I have looked at the Resara http://www.resara.com/ thin client.  It is a turnkey solution that is not free and open source.  It is a very stable solution with excellent support.  I am looking at the Resara solution because I find I have less time these days to develop and support these types of service at my school.

Bob Sargent
Technology Coordinator
Waits River Valley School