In a previous tip, I discussed an organization that, due to a variety of issues, ended up with an unrecoverable information store. The recovery solution consisted of exporting the contents of each user's cached OST file to a PST file and then deleting and recreating the information store before importing the PST files back into the store.
If you ever find yourself in a situation in which restoring Exchange from the local OST files is your only option, make sure you do things in the right order. Failure to do so isn't the end of the world, but could make it necessary to purchase additional third-party utilities and could extend the amount of time it takes to recover.
Specifically, keep in mind that the OST file is tied to the user's Exchange mailbox. If you're dealing with a corrupt information store database, don't delete it until you've first logged into each users Outlook client and exported the contents of the OST file to PST. If you delete the mailbox store first, Outlook will connect to the new, empty mailbox and, even if the new mailbox has the same name, Outlook will be unable to use the OST file that was associated with the old mailbox.
Of course, there are a ton of third-party utilities available that will allow you to convert the contents of an OST file to a PST without using Outlook, but, in my book, it's always better to have multiple options for recovering in this kind of situation, so make a best effort to use the Outlook method before moving on to other utilities.