Pst-files are not part of a roaming profile and for good reasons. One of
them is that logon and logoff time will be much much longer as pst-files are
usually quite big. Impatient users will experience this as an hang and
simply reset the computer instead resulting which could result in a total
loss of the pst-file.

In a managed environment you really don't want to use pst-files. Consider
using a server side archiving solution instead.