I would be careful using PST files. Depending on what version you have they can become unstable after growing larger then 2 or 20GB. I just went through a demonstration of Office 365 and it could be a good fit for small/medium size offices where resources are limited, and they let you do archiving (for a small fee) which is great tool for the E-Discovery world that we are in today.
Also regarding the other post of saving emails, if you save them, then make sure you delete them in your email program or your IT Dept. will be backing up duplicate data
-------------------------------------------
Brendan Murphy
Director of IT
Walsh Brothers Inc
Boston MA
-------------------------------------------