A few days ago I decided to enable Krunner's desktop search/strigi implementation - strigi indexing was not enabled before.
It might have slowed down Medusa a bit, but the most noticeable feature was my 30GB home partition running constantly out of disk space.
File/directory size analysis with du -h --max-depth=2 | grep '^[5-9][0-9]\{2\}M\|[0-9]G' > listfile.txt and ls -lha | grep 'G' ~ found the culprit: a whopping 13 GB .xsession-errors file. This is a well-known problem, apparently Nepomuk/Soprano is pretty garrulous.
First aid: delete the file and reboot. For a more permanent workaround, a poster in this discussion suggests linking .xsession-errors to /dev/null via an autostart shell script. As an alternative, I'd suggest adding ln -sf /dev/null /home/<yourusername>/.xsession-errors to your ~/.bashrc.
As an aside: for anyone puzzled by the redland/sesame backend debate, the current backend is virtuoso and supposed to be faster than any of the above.
