.OST file and DRP Question

Do any of you guys utilize .OST (Offline cache) on your Exchange/Outlook clients as part of a recovery process. Example, MS Exchange server goes down- clients still access emails in InfoStore and Contacts offline, until Exchange comes back up?
Also, does anyone have an Exchange box ready to go in case of extreme problems?
I am trying to pull a Disaster Revoery Plan together with our Exchange server 5.5. Your thoughts would be helpful.