I used a Sun Ray for two summers when interning at Sun Labs in 2002 and 2003. They were kind of awesome and kind of sucked at the same time. First, the display wasn't that great for the time, and they were expensive for what you got. Second, we had ours hooked up to (one of) the labs' E10ks. Because it was shared amongst many users, some things could get janky under load. One thing in particular is that certain image formats were heavier than others, and the crappy Firefox at the time could cause jank for multiple users when processing image-heavy webpages.
It was a neat party trick to take your ID card out of your terminal and walk down the hall, put it into someone else's and boom, have your session, but that was more rare than you might think.
All in all I think I would prefer a workstation.
Admins on the other hand, probably preferred these. If the thin clients were more like $100-200, this would have taken over the world. But they were more like $1000+. Sun considered that a bargain. Which shows you what Sun thought consumers.