Akonadi uses a MySQL db which is kept in your home directory to keep everything - mailbox index, your contacts, calendars etc. MySQL frequently has issues on NFS, and isn't supported to work with that.
Strangely I cannot find any official comment from the KDE or KDE-pim projects about what has happened here, even though the forced adoption of this immature technology has caused a lot if ire withing the community. As a single example I give you http://comments.gmane.org/gmane.comp.kde.devel.pim/33089 but there are thousands more that you will find if you ever try and google a solution to the various and sundry Akonadi/Strigi/Nepomuk issues that people are having.
