Amarok was basically unusable on my shared system. I moved from using SQLite3 (stored in ~/.kde/share/apps/amarok/collection.db ) to MySQL (running on the same host, stored in /var/lib/mysql - different partitions). The process for porting from SQLite3 to MySQL was straightforward. Performance has improved greatly.

This may be due to the /home file system needing a good fsck and defrag, or due to SQLite3 vs MySQL performance, I can't tell at this point.