I don’t think that there will be too much fallout from this move, since most folks would have stuck to other kinds of Web-based calendar system as Ovi Calendar wasn’t really the first choice for most folks. While Ovi Calendar was decent in its own right, there was always this long running issue with synchronization failure – it either fails to work as intended, or does even worse by wiping content off your handset (unintentionally, of course) during the synchronization process.
Ovi Calendar will stop being accessible via the Web from August 31st onwards, although all content on your smartphone will still remain, and you can perform syncs and backups. It isn’t even going to move over to an upcoming Nokia device – it will instead be dead and buried. Hopefully there is a way to export all that data to a different calendar service…