Exchange 2007 and Public Folders
It appears that the rumors of the demise of Public Folders has been greatly exaggerated. Per the Exchange Team Blog, Exchange 12 (Exchange 2007) will continue to support public folders and will actually improve manageability.
Personally, I recommend using SharePoint Services (Windows SharePoint Services - WSS) and SharePoint Portal Server (SPS) for collaborate application development for all future in-house initiatives and strongly suggest moving any public folder applications that you might have to WSS or SPS in the near future.
The writing is on the wall that WSS and SPS are the way to do this in the future.