OST Files and PST files

[Dave]

Hi All.
We support 68 sites / 1200 users, from our MS Exchange Server. We
have had problems with OST files not truely representing/synchronizing
the mailbox.
One of our more advanced users has created and is now using a PST file
locally instead of an offline OST file.
I was wondering if PST files are the better route to go, it appears
that his mailbox has reduced in size considerably on the Server since
he started using the PST file.

Any info regarding these files and stratagies would be greatly
appreciated.

Dave