I'm posting this in case some of you are getting a pop-up window when you log in to KDE 4.6.1 telling you that the 'Nepomuk service stub' has crashed, and you are putting up with it as an inconvenience.
Irritating, isn't it?
It's reported in KDE Bugzilla Bug Report No. 267666
but the solution given in Comment #1 is not obvious to the Linux neophyte.
Basically, what you have to do is:
1. Navigate to Kickoff > System Settings > Desktop Search.
2. Untick 'Enable Strigi Desktop File Indexer' and 'Enable Nepomuk Semantic Desktop' and click 'Apply' (keep the window open).
3. Delete the file ~/.kde4/share/apps/nepomuk/repository/main/data/virtuosobackend/soprano-virtuoso.trx
4. Tick 'Enable Strigi Desktop File Indexer' and 'Enable Nepomuk Semantic Desktop' and click 'Apply' and close the window.
5. Log out of KDE and back in again. Hopefully you should not get the KDE crash pop-up window any more.