The difficulties of users of Coda will depend on how many they are, and on how complex their usage is. I feel Coda is certainly up to supporting, say, a hundred users who use it as a shared file system. It would be relatively easy to set up a cell with the users' home directories in Coda, though I don't know if this has been done yet. If you have many users, especially if they want their own groups, if their filestore has to be backed up, and so on, I imagine this would be quite a headache for the system administrator. In short, I don't know whether Coda is up to handling very large numbers of users, but I think it can deal with a hundred.
Because Coda's file semantics differ slightly from those of plain Unix file systems, you might think users need to learn a lot before they are turned loose on the system. I fint this is not so: beginners do not need to learn everything, unless perhaps they want to use disconnected operation. The number of utilities which will have problems because of Coda's non-classical-Unix semantics is surprisingly small.
I'm a little concerned about using Coda on workstations which have several simultaneous users. There are a number of subcommands of cfs which, for example, throw away any changes which happen not to have got transmitted to the servers. I would be less anxious if these were removed from cfs and placed in another utility, perhaps one that only Coda system administrators or only root could use.