I loathe them.
I worked for A Large Government Agency that was deeep into the Sun ecosystem and was using a Sparcstation 5 workstation well into early 2000s running GIS, RF analysis, and report writing tools. It was a 24x7 operation with shifts of users logging in and out every 12 hours and those systems were never not in use and never powered off. They, and the software, were practically flawless.
Then we switched to Sun Rays. For "security" and "cost". It was a disaster. The latency even just across a couple of floors, was terrible. They spent more on titanically large, best-of-the-best, fantastically equipped servers and immediately the several hundred users trying to use them overwhelmed disk I/O, network throughput, and memory capacity.
We had to log in in staggered blocks, with 5-minute gaps between groups of 20 or so people inserting their cards.
My memory is starting to fade but I recall there being absurd amounts of downtime, with weekly briefings about capacity upgrades and equipment installs and the constant presence of network and server installers dragging pallet jacks and ladders around the facility.
"Oh the servers were underspecc.." NO. They were not. They were literally and actually millions upon millions of dollars of the absolute best and most capable servers Sun sold. We had Sun employees working in our facility. They had an open spigot of cash flowing from the Large Government Agency directly into their accounts to do carte blanche whatever they needed to do to make it work.
If the servers were over-subscribed it was because the ability to deploy that much capacity did not exist for any, infinite, amount of money and Sun knowingly and willingly ripped us off.
It never worked. The experiment made my professional life a living hell for several years.
In 2005-2006 they gave up and moved to Dell workstations running Windows XP professional using thrown-together Java or X11 versions of all of the applications.
Except for capacitors exploding at random intervals, it was "fine".
Moving from ancient vector-graphics GIS tools to Google Earth blew my mind though...
edit: literally never, ever, did anyone need the ability to pull their card out, walk over to another person's desk, and say, "Well hey Jim take a look at this!" and move their session.