Public Folders are used in earlier versions of Microsoft Exchange Server to store free/busy data and files. From Microsoft Exchange Server 2007, free/busy data is no longer stored in public folders. It’s recommend that you do not store files in public folders in Exchange 2007. Instead, consider using Microsoft Office SharePoint, or Windows SharePoint Services. Public folders are included and supported in Exchange 2007 and 2010. However, future releases of Microsoft Exchange might not include public folders. You can visit http://blogs.technet.com/b/exchange/archive/2006/02/20/419994.aspx. Also, you can refer MS Exchange team blog have posted the updated public folder guidance for versions of Exchange past Exchange 2007.
So, what are my options?
If you're building something new, you should look at the requirements and building on the SharePoint Technologies platform:
+ Starting with Exchange 2007, we recommend that applications use the Availability service to provide free/busy data for Exchange mailbox users. Windows SharePoint Services replaces the file sharing functionality that public folders provide. You must redesign applications that use public folders to use Exchange Web Services.
+ Also consider redesigning custom applications as early as possible as future versions of Microsoft Exchange may not contain public folders.
+ In addition to that you can refer the wonderful blogpost by Joel.