http://www.microsoft.com/technet/events/winter/tnq30007.asp
http://www.optimal.de/service/download/whitepapers/bestpr2.htm
There is a lot of information and case studies on the network. A few things: PST is not good unless the client is permanently connecting using a slow connection, even then consider using OST's instead. On PST's you cannot reinforce the size limit...
Best design would have the system, logs and database volumes residing on completely separate volumes.
Size: we have broken our user bunch in 3 groups, 50, 75 and 100 Mb limits. You can setup levels for warning, block send and block send and receive (we have 25Mb increments). Put limits also on attachments(1-5Mb, depending on your Internet link)
Back-up: we're usingnative ntbackup with no problems, but there are some better back-up solutions (allow you to restore individual mailboxes).
If you size it and configure it right from the beginning, there is little that will go wrong. We've been running it for over3 years now, in a multisite configuration and had no major headaches yet. It survived one harware upgrade and one migration.
I hope this helps.
Regards,
Radu
