John (disconnected), problem of rendering international symbols is not related with a 'Visual Rich Text Editor' (TinyMCE), which is responsible just for input of such. also, it's not generally related with fonts used.
as I already stated above, I assume that during upgrade/repair/etc some cluster of blogs has been transfered into a database which accidently has been created not in the 'utf-8' CHARACTER SET (as it must be in the wp.com case), but rather generic 'latin-1' (which is setup defaults for the DBMS used by wordpress).
question marks in the diamonds instead of international characters is a sure sign of it.
all that further hype with lost blogs' content is probably related with attempts to restore last (properly encoded) backed up entries to new DB(s) which in its turn could cause another major fault.
well, running an online service with 1,000s users is a very_hard_task.