Thin clients can be rockets
John Brown wrote, "We did a deployment for a client a couple of years ago. Upwards of 800 locations around the UK. As we got near the end of the deployment it was visibly obvious at 9am when everyone was logging in that it was getting slower and slower the more offices were converted. Day to day use may have been ok, but the system couldn't cope with the peak demand times."
That's trivial to deal with. It's a predictable slow down and can be easily solved by installing local caches and faster networks. The designer didn't do his maths. One trivial solution is to remotely set the clients to boot a few minutes before office hours. Add a few servers for log-in peaks. I've seen M$'s OS take 2 minutes to give a usable desktop on legacy PCs. I've seen thin clients open a session in 5s, even less if the session is left in RAM on the server. Every solution has scaling problems. The legacy PC is just about the worst solution for many usage cases. The worst case I've seen of legacy PCs besides complete failure to boot was a lady who would go to her desk and fire her PC up so it would be ready by the time she had her first cup of coffee. After that, it took 2m per click for the PC to respond. How convenient/efficient/effective was that? She was amazing. Despite the performance of her PC she still got her work done but imagine how much better she could have done her other tasks if she was not always wait, waiting, please waiting... She wouldn't permit me to install GNU/Linux until she had completed her contract when the identical hardware turned into a rocket. It was still a thick client but she could have been running software on a brand new powerful server instead of an 8 year old PC as a thin client. Until you've seen thin clients done properly, don't state they can't do the job.