You're right, about the slash. I use that and colon interchangeably, since at the UI level one is represented by the other in the filesystem. The issue I mentioned is still the same though.
You'll find that some apps, by default, create folders with slashes - which gets colons at the disk level. Bento is one example. I don't use it regularly anymore, but I had some data from previous sessions. When these ended up on the ReadyNAS they could no longer be removed. I might have been able to telnet into the ReadyNAS and remove them from there, but I didn't get around to trying that. They could not be removed by Windows nor Mac OS, so I had to blast the entire share from the ReadyNAS control panel. Thankfully it was on a backup share.
Accented characters are an issue for me because I deal with customer license files that have accents, stuff friends in Europe send me and of course song titles on MP3 and FLAC files.
Getting rid of all the accents, and not using them going forward, would be a far greater compromise than dealing with the maintenance when issues happen. Thankfully it's not often. But it does prevent me from using rsync from the NAS. I can probably initiate on the Mac where I can use the command line to put in the proper iconv arguments. But that defeats one of the big features of the ReadyNAS, which is built-in backup scheduling. Thankfully I rely primarily on Time Machine for my backups - I just like also having an additional one or two backups of the really important stuff. I suppose I can segment the super-important stuff to a hierarchy where no accents or specials are used.