PST Files not Supported over a LAN / WAN
We came across this the other day where Microsoft do not support using PST over a LAN / WAN. For example, you may have your PST on your home directory so you know it is backed up every night.
http://support.microsoft.com/default.aspx/kb/297019/
It seems that the PST files are not designed to be accessed over a network and are therefore slow. Microsoft suggest using OST files.
Something to bare in mind...