Mailbox data can be restored back to the recovery storage group (RSG). It can also be recovered on a hot spare server.
To recover the public folder data, you would need to mount the database on a hot spare server that is isolated from production. Once you have the data back online, you can use ExMerge or Pubmerge to extract the data into .PST files -- then you can import that back into your production mail environment. You should also consider looking into this webcast I did with David Sengupta on this topic of recovery.
Within the standard recovery context, you will lose the public folder data if you try to recover it through the Mailbox Recovery Center in Exchange System Manager, because it only allows you to mount mailbox stores.
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This was first published in September 2005